I have 3 Thorowgood saddles. 2 dressage and an AP broadback.
I bought 2 of them used after stalking the internet for quite awhile–it can be hard to find the new T4 models in the US used, because everyone loves them–and bought the other one on Smartpak, because I wanted the broadback model for my barrel-backed horse and gave up on finding it used.
In terms of quality for price, IMO they can’t be beat. I agree that they ride like a more expensive saddle.
They do run roomy due to the open seat. I have an 18" T4 high wither dressage. I bought that size to accommodate my long femur – with 17.5" saddles in most other brands, my knee ends up over the flap. However, with this saddle I actually feel like I have too much room. It is also pretty long front to back, so if you have a short-coupled horse it’s something to keep an eye on. I picked up a 17" T4 just last week, because somebody local to me was selling it for just $150 and I knew if I didn’t like it I could resell it for more. But I think I like the 17" better because it puts me closer to my horses’s center of gravity and I might end up selling the 18". With the velcro blocks, I’m able to move them just enough so that I have enough room for my long femur, too. I basically have the blocks 1/3 on the saddle and 2/3 sticking off the front 
You asked about twist. My 17" dressage saddle is a slightly older version of the T4 and I feel like it has a narrower twist than my 2 newer ones. But that could just be my imagination. My 18" feels like it has a wide twist, but maybe that’s just because it’s a big big saddle.
Love the wool flocking. Love the adjustable/interchangeable gullet plates. Love the adjustable knee blocks. Love the adjustable billet rigging. My horses go well in them.
Overall I think I could still find a better ride if I had a higher budget – say $2500 – but in the sub-$1500 range, you sure can do a lot worse. Before my thorowgoods, I’ve gone through 2 albions, 2 stubbens, and 2 sommers. All great saddles but not great for my particular needs.
I found the broadback model to be good but not great for my wide-back, almost-no-withers arab mare. She really needs a true hoop tree. But it’s a sufficient stopgap and the resale value on these is great right now.
If you buy one, make sure to get the T4, T6, or T8 – those are the ones with the adjustable gullet.