The Little Dot line of headphone amps represent what is possible when a Chinese production amp doesn't cut corners on build quality and engineering. This amp has my vote as the best desktop hybrid amp in the price range.
 
Build/Design
 
The build quality is very solid; the housing is all metal with a very smooth and clean-looking volume knob. The amp is also quite heavy. The design is very plain however, which is fine, but a little boring. 
 
What really stands out in the design department is the choice of tube socket/settings (WE408A, EF92, and EF95). Both WE408A's and EF95's are very affordable and effective replacements for the unimpressive stock 6JI's. The 6ZH1P-EV Voshkhods for example are available through eBay from Russia or Ukraine for less than 15USD per NOS pair. Another favorite of mine is the GE JAN5654, which I found for 3USD for a NOS pair! If you want to splurge, EF92 Mullards (M8161) are also a great option. But to play devil's advocate, a user on AudioKarma ran some tests on the circuit and concluded that tubes contribute next to nothing to the circuit. 
 
Along the same lines, the op-amp can also be rolled since the LDI+ has a no-solder DIP-8 slot installed rather than a surface mounted or through-hole soldered op-amp. Personally, I think op-amp rolling is a waste of time when comparing op-amps above the 1USD mark. For example, an OPA2134 (~4USD) is hard to distinguished from an OPA2107 (~15USD) or MUSE02 (~30-70USD) but is probably better than the stock, which is worth less than a dollar.
 
Sound Quality
 
The sound you get is somewhat dictated by the tube you roll since this hybrid amp does rely on the tubes for color (whereas most of the amplification is done by the solid state components). Whatever tubes you roll however, the sound is very clear and balanced, which is what you want out of an amp barring any coloration you desire from the tubes. Detail is also great on this amp, especially with a good pair of open or semi-open cans like the DT880. Higher impedance headphones also benefit since the output impedance is said to be around 30 Ohms. A quick overview of tube impressions and reviews are available here: http://www.head-fi.org/t/364043/little-dot-i-tube-rolling
 
The only demerit for this amp is the relatively low power compared to other amps in the price range. For my 250 Ohm DT880's, it takes about 70-80% on the volume knob to get good volume for modern mainstream recordings and full volume to enjoy classical recordings (which tend to be much lower volume recordings). The gain can apparently be changed internally, but this is annoying if you switch between different headphones of different impedances.
 
Overall, I love this amp and powers my home headphone setup. A great option for all except the most frugal shoppers of HiFi devices.

The Bravo V2 is an attractive and inexpensive "pseudo-tube/hybrid" amp that is easily accessible to beginner DIYers if modifications are desired (which they definitely are as I will expand on later). 
 
I'll review both the stock unit as well as modified amp although the star rating is for the stock unit. The modded unit would be a 3.5 - 4 star rating.
 
Build/Design
 
The V2 is a small desktop amp (8 x 8 x 3.5 cm approximately) with exposed sides and a clear plexiglass top and bottom plate. It is very attractive and easy to access for mods, but that's where the build/design strengths end. The PCB is very cheap and the stock components are very cheap. For example, the amp is powered by 24V but the power cap is only rated at 25V, leaving little room for overvoltage protection. Replacing this cap with a 35V cap is good preventative measure. The is also a sound popping sound upon power ON, which can be fixed with an induction coil and relocation of the switch; I'm no electrical engineer, but this is bad circuit design I would think.
 
The blue LED is obnoxious in my opinion and is an eye-sore. You can either short it to turn it off or replace it with another LED of your choice.
 
Also, this is what many consider a pseudo-tube amp since the tube itself does very little of the amplification and is largely used a pre-amp stage for coloring/warming the sound. Other hybrids utilize the tubes a bit more and pure tube amps run crazy high voltages.
 
Sound
 
The stock unit does not sound very good. The highs are muffled and there is noticeable distortion. Bass heavy songs sounded OK, but everything else sounded muffled and harsh with none of the warmth you might expect from the tube preamp. Replacing the stock tube will help the sound, but the real fix is to replaced the stock IRF630 voltage regulator with a IRF510 or IRL530 regulator instead. This extends the highs and also seemed to reduce distortion. The heat generated form these upgraded regulators however is higher, so it may be wise to upgrade the LM317's to LM317A's as a preventative measure. After switching to an IRF510, the heat sink measured 70-75C after 30 minutes of operation (I used an IR laser thermometer). Replacing the output caps with 25V/2200uF caps are said o improve the lower frequencies, but that's debatable depending on who you ask.
 
Value
 
At under 70USD, this is a great way to get your feet wet when it comes to DIY audio devices. If however, you want bargain sound under 100USD without doing any mods, go with a solid state amp like the Schiit Magni or a FiiO E-Series amp. 
 
In closing, I think this is a nice introductory amp although the sound quality was never stellar even with a full suite of modifications. As I mentioned earlier, this is a great DIYer's amp although the cheap PCB is terrible for desoldering. It would be great if this amp was offered as a kit for home assembly (that way, you only need to solder once and include any upgraded components the first time around), which would further drive down cost.

I've owned two pairs of these over the last 10 years (one channel on the first pair died) and I've used them without an amp or any knowledge of audio electronics. Essentially, they were the first pair of decent headphones I've experienced prior to entering the world of HiFi only recently.
 
The ones I've owned were 64 Ohm but performed admirably at >80% volume on most audio sources. They improve noticeably with a headphone amp.
 
Sound
 
This is a bass heavy headphone and is well suited to movies, action games, and bass-heavy music genres. Bass-heavy electronic and hip-hop tracks are like personal earthquakes with these headphones. Having said that, bass can get muddy on certain tracks if volume is high. Mids are recessed and treble is usually clear with some occasional harsh/shrill-ness depending on the frequency. I'm into classical music and these don't do as well for violin and piano sonatas and concertos due to less pronounced mids/highs and a lack of soundstage (these are closed headphones though). Overall, the sound is great something that is <$100.
 
Construction/Aesthetics
 
These are not particularly attractive headphones nor are any of the structural components high-end (no metal used on the body except maybe the core of the head band). My first pair broke even though it rarely left my house and I took very good care of it. The second pair has lasted much longer so this may be an individual issue between pairs. The collapse-ability of the headphone makes it more portable than most over-ear headphones, which is a plus.
 
Definitely recommended as an entry-level bass-head can.