Pros: build, sound, cost
Cons: coiled cable, FR i'm not entirely used to yet
Comparing these to my Philips L1 and my Beyer T1 they have a lot more mid-bass through midrange and are slightly tilted toward the high. They sound great but quite a bit different sound signature which I need to get used to. My other headphones are T5p which I have yet to compare them to and Ety ER-4s. In general all my previous phones have a less aggressive sound to them. Less mid-bass in your face. Very very efficient, almost double the volume as the L1 and over triple the volume of the T1. It puts a lot of music and detail across the entire spectrum in your head not light on any frequency and not missing any detail. As I said it can be a little tiring after coming from the L1 or T1 which are much more laid back sounding.
Build is top notch for the price, very solid. Cable is a bit over-engineered especially if you are planning to use this portably. I only wish it came with a straight 4' cable rather then the coiled 9' one since I will be using it on the road but one nice thing is the cable is a simple 3.5mm male to male so you can replace it with anything you want. I will replace it with a simple super light weight $5 3' off amazon. I'm one of those people who doesn't see great value though in thick or heavy cabling. Super-silver oxygen free pure copper it all sounds the same to me in lengths under 10 feet.
Will have to see how the 7520 performs with cabin noise but it does seem to isolate better then the L1 and I am guessing the stronger midrange and bass might come through better with more background noise. I can't stand the cable of the L1 which is one of the big reasons I was looking for something different. Not sure if I will sell the L1 even though this was meant to replace it because I also like that signature and I bought that at the intro price rather then the steep discount now being offered online. It just isn't worth the loss in value to let go of seeing as they still sound great, will probably just re-cable them.
Edit: After 30 hours of burn in with white and pink noise they sound much more balanced. The mid-bass hump seems to have diminished and both ends have opened up. Getting used to the sound as well and they are starting to really impress me. However my new complaint is that they really need another quarter inch of ear cushion thickness to help soften the feel and also to lift the drivers a bit so they aren't touching your ear like mine do. Not quite as soft (plush or cushy) feeling against the ears as I am used to with either of the L1 or T1 or T5p. I am starting to get used to that as well but it would really help in terms of comfort and even give a better seal to have slightly thicker pads which I don't think would have cost more or cause any sound quality issues. In fact I think adding this foam would perhaps improve the sound slightly, as I said there is plenty of sound output so distancing the driver slightly from the ear may give a more laid back feel. If anyone knows how to make a mod to add say a quarter inch of memory foam behind the stock pads I am all ears. Also if anyone has any comments regarding possibly removing the light cloth mesh inside the cups between my ears and the driver I am considering that as well. Currently my ears touch the mesh and it is a little aggravating.