I have a Sony MZ-R900, which was a top of the line model a year or two ago. I love the thing, to be honest, but it has fallen out of use in recent times, and has been replaced by an iPod as my primary portable. Others have posted a lot of the pros, such as good sound quality, portability, and battery life -- and these things are true, but here are some things you should be aware of if you intend to make a move to MD.
The first is the cost and inconvenience(more on convenience below) of media. The average price for good quality discs is around $3-$4. You can find them for less, but I've found that you get what you pay for in this realm. So while the base cost of an MD player might seem on par with a good PCDP, or even an MP3 player, the actual cost is going to be equal with an expensive HD MP3 player, and much more than a PCDP since the MP3 players come with all the storage in the price, and obviously the PCDP plays what you already own.
As far as quality goes, I would actually rate it in the middle. PCDP on the bottom, despite the far superior format, because there are no good outputs on modern players these days. MD generally has much better sound, but MP3 (I use the term to classify all digital players, whether you play AAC or Ogg Vorbis, raw PCM, or whatever) can actually be superior to all of them due to variable bitrate encoding and some that even play FLAC, a lossless compression. A good MP3 player can put out surprisingly impressive sound (class C, according to a recent Stereophile review).
The next thing you have to watch out for is NetMD in modern MD players. They promise extremely fast transfers. Top of the line Sony players can transfer LP4 files at 64x, and LP2 at 32x. The multiplier being based on a real time transfer. However, and this is a big however, the quality of the files being transferred at this speed are dubious at best, and the current software used to transfer them is riddled with obnoxious "copy protection" schemes. The main problem with using LP2/4 is that they are highly compressed using ATRAC. So when you move your MP3s or other digital files with it, you suffer the consequences of transencoding. Artifacts from multiple psychoacoustic models that do not regard each other, and so on. Just as any digital format afficiendo would never take an MP3 and turn it into an AAC without very careful consideration, one should approach the MP3 to ATRAC conversion process with equal caution. Additionally you are at the mercy of a single vendor for ATRAC encoding and original file decoding, where with other digital formats, you can pick and choose based on quality. There is no LAME in the ATRAC world.
So for anyone who is really concerned with quality, they will rarely mess with LP2 or LP4, meaning you are stuck with real time transfers. This is a slow, slow process for moving your collection from CD, and requires a CD player with optical out for the best quality. Some Sony models come with a USB "soundcard" with an optical out, letting you use a computer to transfer.
The alternative to that is getting a proper deck MD player/recorder. This is an expensive solution, but it gives you much better quality recordings, and some integrated CD/MD decks offer 2x and 4x transfer rates at full quality. If you are serious about MD, getting a deck for recording is something to consider.
Portability is the next issue. While one would think that an MD collection would take up much less space than a CD collection, I have found this to not really be the case. If you carry your CDs around in a portfolio without the jewel cases, you can actually tote around an impressive amount of music. Due to the MD's thickness being inside its own integrated jewel case, the collection cannot be compressed much. In a typical day, I was taking out roughly the same amount of music for use with my MD that I had been with my CD player. This means carefully selecting what I
think I will wish to listen to during the day. This is where a hard drive MP3 player clearly wins, as with the larger capacity models, one can carry around their entire collection in a device the size of a deck of playing cards, at quality levels that are on par, or exceed the alternatives. In fact, I found the things to be so portable that I went ahead and got a miniature amp and case (from HeadRoom) to give me even better portable quality, since I was no longer toting around a portfolio of media.
The next thing to be aware of is ATRAC itself, and this is really a matter of taste. For me it is a negative, others really like the sound it puts out. The main reason I've stopped using MD is because I felt that ATRAC sounded very lifeless. At first audition, I was very impressed, partially because I had only compared it to portable CD, and it was clearly so much better. But as time went on I realized just how little soul the music had. While all of the sounds are there, the life is sucked out of it for me. This is just something you'll have to figure out for yourself since everyone's ears (and equipment) are different.
Another person already brought it up, but I'll add my vote as well, and that is the weak output signal. Doubtlessly this is part of how they get their battery time. If you plan on using low efficiency headphones, such as the Etys, you'll be hurting for a portable amp. With the ER4S, the sound out of the R900 was a little too soft, and had a thin quality. Once I switched it over to Line Out (that model has an integrated software switch on a single jack, kind of weird if you ask me) and plugged it into a Cosmic -- well then that is a different story entirely. The sound coming out of there was very strong, and that is of course when I started hearing all of the limitations of ATRAC. Though I'll be the first to admit that an ER4S/Cosmic combination was a rather remorseless way to treat my MD. That kit will tear a deck CD player up. I have no experience with using high efficiency headphones, other than the ones supplied with the player, and -- eh -- well you know the type of dung they bundle with players.
I am getting down to the end of my list. This is another one that depends entirely on the person. If you have larger hands, most of these players have
very tiny controls. Though they are better than they used to be. See if you can find a picture of the model I have somewhere. That thing has buttons you practically need a toothpick and an jeweler's loupe to manipulate! If you buy used, that is something to look out for. Today's MD players, at least from what they look like on the website, appear to be a bit more intelligently designed.
And last but not least: You are at the mercy of Sony.
Masters of all things paranoid schizophrenic when it comes to lock in schemes and copy protections. While you can work around some of the flaws in NetMD today, it is certainly an inconvenience, and who knows what the future will hold.
Oh, one other thing. I saw somebody say that the future of MD is strong based on the size of the market outside of the US. However, I am not convinced that it is a long-term solution these days. NetMD was a, in my opinion, failed attempt to counter the MP3 player explosion, and the original MD format is starting to show its age, not only in quality, but capacity. The single reason that I have doubts about the future of the format though, is that I have seen Sony's new direction in optical disc storage, and that is UMP, not MD. While MD will certainly last a while longer on sheer market inertia, I do think it will eventually be replaced by either MP3, or these new UMP discs.
Anyway, there you go. As I said at the beginning. I actually like MD. There is something unqualitatively fun about the format, least of all the looks you get in public. It is surprising just how little people are aware of it in the US. They see those little discs and think you have some futuristic thing, then when you tell them it is decade old tech, they scratch their heads. MD has its definite advantages in some cases. I would buy from a place that has a no-questions 30 day return policy. Get some media, and see how it works for you. If you don't like it, you can return the gear, and use the money to get a ton of new CDs to listen to.
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Oh one quick other thing, this is actually a pro. The only thing I still use my MD player for is something a lot of people forget about, being so far away from the distant realms of the tape culture. That is field recording! Get a powered microphone and make your own environment samplings.
