I picked these up after I accidentally broke my pair of A-Jays Ones, which I loved. I figured if I was going to buy another pair, it might as well have the iPhone mic built in. I wound up returning them and going for another pair of the Ones. Here's the rundown...
THE GOOD
The Fours have the same terrific design as the Ones, and the mic/control is terrific. The buttons are easy to find and the different shapes make them easy to differentiate. The whole setup really looks like these should be what come with the iPhone instead of Apple's stock headset. I didn't really care about the adapters that came with the Twos and Threes, so the fact that they weren't included here didn't really bother me.
THE BAD
After unpacking what I thought was going to be the perfect pair of headphones, I put them on and was immediately disappointed in the lack of bass. My Ones had great bass. It was strong, but not overwhelming. The bass coming out of the Fours is almost nonexistent. I had read some other reviews saying that the phones were tuned to amplify voice frequencies, but there really is a massive drop-off in bass from the Ones, and it was something I couldn't get past. It unfortunately reminded me of listening to my laptop speakers. I even tried two pairs to make sure that I didn't get a bad set.
THE BOTTOM LINE
Personally I prefer the Ones. If they could make a set of headphones that had the sound quality of the Ones and the features of the Fours, I would be a very happy camper. In the mean time though, I'll settle for my Ones for music and my Bluetooth for calls.