I can tell you that I like v534 much better that v526.
I upgraded to the official AT&T 526. Here's why I decided to upgrade to v534 from Bell Mobility:
1. Several times per day when I try to open an email from the notifications list, the phone freezes. A battery pull will keep going. If I wait it out, it takes almost 30 min, then gives App Erro 602 and then I pull the battery.
2. If there is more than 1 email, the first in the notification area is in white, the others are black and overlap, unreadable.
3. During of heavy browser use, it begins to "forget" to render some text. The problem gets worse. The space is just there, but no text. Selecting doesn't show it, nor does copy and paste elsewhere. Eventually, Google looks like one big page of underlines. Battery pulls will correct it, but it happens again, that is if I get to play with it long enough (see #1).
v534 kicks v526's behind. Even better battery life

hone: and much quicker response time. No lag when thumbing thru pics as well. Have not had the email issues or browser problems with forgetting to render text.