Flipping through the gallery I saw at least two photos of barns in use that had high doors in the row also. Not all were low. Which tells you something: planners realize not all horses earn the privilege of low fronts.
I’m about to build a new barn and will be installing a version of the low-front stalls (from either Lucas or Classic Equine - still deciding between the two).
In my current barn I have wooden stalls with full-height walls on either side of a “low” door - you can see a pic at http://www.fridayschildfarm.com/facilities. I have babies, young horses, and old horses, and I’ve never had a horse really try to jump over the door. The low-front stalls will be at least the same height if not slightly higher at the lowest point, so it’s not something I’m worried about. If a horse really wants to get out of the stall they will find a way, and I’d rather them jump out hopefully unharmed as opposed to getting stuck in a narrow opening. I do have a 16’ aisle in my current barn and will have the same in the new barn, so leaning out and biting at horses in the aisle has never been an issue either.
I’m personally not a fan of the full height doors with drop-down grills or narrower openings in the middle. In my experience, horses tend to whack their heads when reaching in/out, and it’s not as open or airy. I think in general the more open the stalls are and the more the horses can see each other the more relaxed everyone is. But of course like others have said it depends on the individual horses. I think it just comes down to your personal preference and what you think will work best for your horses.
As they are a custom design business, You can have the solid stall sides as high as you want, with sliding doors as high as the walls. Top that with steel bars , stall top and door top. Horses can see out, you can see in, and everyone will be happy.-Except for the 14.2 pony.