We used literally thousands of gallons of Unibond before we bought our hot press; UB isn't really designed for those kinds of temps so we use National Casein 750 now, mostly, though still use some UB for vac press stuff. Here's my $.02:
A lot of it comes down to application and preference. The downsides of PPR (and it's all the same stuff, regardless of whom you buy it from) are: shelf life, mixing, and consistency. I always found PPR -- even fresh material -- grainy and a PITA to mix. When spread thin on a panel for veneering it often seemed to pull or fisheye in a way that UB does not. Being able to vary catalyst ratio to achieve different cure times was a good feature for Unibond, and achievable cure time is faster than with PPR. I also like the different colored catalysts available for Unibond, but that's not essential.
Downsides for Unibond are smell/fumes (though that's much better since the reformulation) and, of course, cost. I've never minded paying a premium for a very reliable product, but that is a personal decision. I believe we were one of the biggest users of Unibond and we never had a failure due to the adhesive. Not ever. How much is that worth?
As they say in the car commercials and online fora, YMMV!
John Costin
Veneer Services Unlimited
vsu@gwi.net
(207)985-7221
Custom Veneering for the Woodworking Industry