Pro Brass is more useable than core. The extra microphones are quite helpful and Pro has several very nice additional instruments.
I use Pro Brass to supplement SSB. It has additional instruments, muted shorts, and some other useful articulations that are missing in SSB. At full price it is a bit pricey as a supplement, but on a sale it made sense and I've found the Studio Brass instruments sit reasonably well with SSB and without a lot of futzing. So for me it's working for what I bought it to do.
Overall, I find the library uneven, and I wouldn't recommend it to serve as the main brass library. Many of the sustains have bumpy transitions between dynamic layers, and there is often unpleasantness in the sound that requires EQing to tame. Out of the box the dynamic levels of the shorts don't match the longs very well (this is true of the whole Studio series as far I can tell), and they don't map to other SF libraries so you have to either program a new velocity curve for the Studio instruments or completely rework the midi. There are also some real odd ball samples in the set. These can be effective as one-shots but when you get that same quirky sample every time it can make the library something of a challenge to use if it's your primary brass library.
As I said, it serves my purposes of supplementing SSB but if I had bought it to be my core brass library, I would still be looking to pick something in its stead.
ETA:
Personally, I think the horns are the least convincing patches in the library (though the stopped patches are go as are some of the extra articulations). I don't mind the trumpet (though I think there are better trumpets out there), but some of the worst odd-ball samples are in the solo Trumpet 2 legato.