I have recently upgraded my 712CE to ES2 and to my ears and in my opinion it has completely fixed the "hot B string" issue of the ES1 (I used to put little bits of metal plate between the frets on the fretboard, over the pickup and under the B string, which helped quite a bit). With the ES2 if you want you can also adjust the volume balance between the top 2, middle 2 and lower 2 strings by adjusting the "allen" screws in the bridge. Again, in my opinion, it is worth the cost. As well as the new pickup don't forget you get a "Refresh" package as well. I guess they have to remove the neck to take out the old under neck magnetic pickup but my guitar was old enough (2001) to justify upgrading to a "Revive" package with fret dress and neck reset (with a couple of ding repairs) and it came back looking and playing pretty much as new. This was done in Amsterdam.
A slight word of caution is that all these things are subjective and it's possible you may not be as impressed as I was, but in general opinions on the ES2 are very favourable. The ES2 is less feedback resistant than the ES1, but I've found it quite manageable and nowhere near as bad as the original Fishman pickup my 712 had before it's first upgrade to ES 1.3.
I hope this helps. Phil
