The youngsters I have seen have, for the most part, been very good movers with good muscling, good elasticity, good front end, bigger body type but also "electric". Some have had shorter necks but I'm not sure if that was from the mare or not. He needs a "typey" mare with some refinement and a good walk.
I don't think he brings power to the hind leg. I think the mare should have an elegant neck that is an appropriate length with a clean throatlatch. I agree that he needs a mare with good type and refinement, and also a good walk. The Quaterbacks I've seen seem to have very good temperaments and rideability.
I must admit I was not part of the whole Quaterback fanfair when he was first licensed. He himself did not do it for me but my opinion changed dramatically this summer!!!! Now this was just a short 1 week experience I had but this summer I got to see at least a dozen or so Quaterback mares at some mare shows in Germany. I liked EVERY one of them. The ones that had already been MPT'd had fantastic scores across the board (even for walk) and very high rideability scores. The ones presented in hand used their bodies very well throuh their backs/ neck/ shoulders. Yes, they did not have 10 walks, but none had absolute horrible walks either. They did not appear to be heavy in type at all...some were a bit shorter in their necks but not so bad to be problematic. They did tend to have the "flashy" front ends but also kept good energy from behind. Harmony Sporthorses had a lovely Quaterback-Sandro Hit mare that I think won the mare show in Dobrock. For us US breeders his frozen is quite proven as well.
Regarding him adding power to the hind leg, I agree with bluehof in that his offspring tend to keep good energy behind. I don't think I would use him specifically to improve the hind end though. Regarding his neck... I don't think that Quaterback himself has such a short neck as much as it is quite thick/heavily muscled, possibly giving it the appearance of being on the shorter side. Perhaps it is just my perception though....
We had three Quaterback offspring in 2009. Two out of the three foals strongly resembled their dams. Only one of the three foals turned out to be a freaky mover, and he is much more like his the dam sire Florencio than Quaterback. This colt is elastic and has one of the quickest hind legs and best canters I have seen on a young horse. Flying change machine at three. It is jaw dropping to watch. He is not an amateur's horse as there is just too much movement to balance.....but it is sure fun to watch.
I haven't seen nearly as many Quaterback youngsters as Nancy, but I have seen 4-5 at Judy Yancey's over the years, as well as about the same number in this area.
Two of the ones I saw were imports, so don't know how they compare to their dams, but they were both really nice. And of the ones I have seen with their dams, I would have to say that most had bigger and more powerful gaits than than their dams. And all appeared to have more substance and bone than their dams, but most of the ones I saw as foals had dams a bit on the refined side.
As for adding power to the hindleg - I think it would depend on the dam. At least two of the mares I saw did not have much power, but the foals definitely seemed to have more power behind. Two other mares had really good strong engines, and the foals did not seem to be more powerful behind, so it is a bit relative to the dam. Regarding the walk, several of the mares were lacking in this area, and the foals were not an improvement, so QB definitely did not add a good walk. OTOH, QB did not kill the walk on foals from mares with good walks.
I would not use him on a big, old style mare, but would certainly use him on a modern type mare with a good neck and good walk.
I have four QBs on the ground and two more coming this spring. The two three year olds have been great to train - very good minds and very teachable. They are very elastic and and elevated in the trot and canter. Both of them have good motors and walks but so do their dams. Their necks could be longer and they are a bit long in the front pasterns. They are all tall ( the yearling is the same size as my two year olds) with good bone. I have been told that QBs are heavy but mine are very much middle framed even the one out of a very large mare.
Softness in pasterns- tendons are not as tight and as a result, are not as upright. Allows for a very nice ride but take away from longevity.
I have a mare that is longer and softer in the pastern that is a great mover, so I am interested in a stallion that passes on correct feet and legs so the foal will have a greater likelihood of inheriting correctness.