At first I wasn't too thrilled with them as even though I stretched them liberally, they still would not stay in tune and didn't sound so hot...however, after a couple of days letting the guitar sit I retuned it and began playing. For some reason, they sounded MUCH better. Doubt if they will last as long as the T-Is, but, again, you're paying a premium price for them.
All in all, I prefer these Pearse strings to the D'Addario Nanos and would purchase them again if my budget didn't allow for the T-Is, which are still my favorite strings for my 12.
They manage to be both warm *and* bright, really letting the 12 string ring out as it is designed to do.
I had a hard time finding the old silk & steels I always used, but now that I've tried the John Pearse Phosphor/Bronze Silks, I'll never go back.