I finally shelled out the cash for one of these today and it worked exactly as I'd hoped it would. It literally adds +2 HP per tick to each paeon song.
So now with Paeon3 being 4 per tick and Paeon4 being 5 per tick, they do 6 and 7 HP per tick, respectively. That's 13 HP per tick for farming and such. It's only a bit more than Regen II which is 12 per tick but with a seemingly small difference.
I don't know if it's just me, but I got the impression that it would regen HP much faster than regular Paeon or Regen. I went from 350 to 900 HP in what seemed like a very short time. More testing is warranted.