I had Tony do the modification to my "new" Red 3. I spent a few months with it in the stock state before I decided to have the transformers put in, so I did have a good base of experience with it before.
When I got it back, I wasn't sure that the difference was huge, but thankfully I had run some tracks through the Red 3 (stereo bus app.) via my Apogee PSX-100 at 48KHz. When I repeated this test with the new transformers in place, I definitely noticed a bit of a difference, though somewhat slight. There seemed to be more of a "sheen" on the tracks. Don't know exactly how to describe it other than that. Slightly smoother (but not attentuated or smeared) high end, perhaps? I did prefer the transformers. It was $550 or so to do it, plus shipping.
Was it worth it? For me, yes. I like the Red 3, transformers or not, and I feel that this gave the compressor a bit of a more unique vibe. I had the money and was interested in hearing the difference, knowing fairly certainly that I wasn't going to hate the end result. If you are looking for a night and day difference, you won't find it by doing this mod. If you don't like the Red 3 as it is now, you probably won't be that much more enamoured with it in the modified state. I certainly like mine now, though.
By the way, Tony was very helpful and prompt. I would definitely do business with him again.
Ian
www.emaginaryrecords.com