They’re built on the same tree, but no, they’re not exactly the same thing.
Why not call the expert on all these brands? Annette Gavin at www.hastilowusa.com. She’s an excellent fitter with Society of Master Saddlers credentials, and she reps for Thorowgood, Hastilow, and Kent and Masters (among other brands). She also knows plenty about Fairfax. She can answer all of your questions.
As for the knee block issue, it’s hard to say what’s going on without seeing the evidence. But here’s some common reasons that that happens:
–Riding in a too-small seat size or a seat architecture that shoves you toward the front of the saddle, which means that your leg is jammed up against the knee block more than it might be in a saddle that’s effectively sized for you.
–Not yet having an effective enough dressage position to ride with your pelvis open and ride with your leg straighter/further back. I see this a lot from eventers or hunter converts: they’re sitting in a dressage saddle like it’s a jump saddle. I’m not criticizing, just saying that this happens a lot, and a big knee block can be incompatible with it. Ironically, I occasionally meet a hunter/eventer convert who LIKES having their jump-saddle-esque leg jammed up against a huge dressage block; it makes them feel secure.
–Even if the saddle fits your body beautifully and you’ve got an awesome dressage position, the block’s shape/placement might just be incompatible with your body shape. This definitely happens. Heck, even if the block fits you well, it might just not be your personal taste or style. I find that if the block fits you well, it practically disappears and you don’t notice it–but even so, some riders prefer the freedom of a more open flap with less blocking.
That said, I’m not sure why you’re worried about this with a Kent and Masters saddle. Some of the have external blocks, but others don’t. Their Moveable Block model is very popular because the blocks are velcro and they’re under the flap, so you can move them (or totally remove them) as you please.