I have a set of "Master Clamp" vices, which I was told were designed by Gearold Ledsome. Maybe they are similar -- low profile, aluminum construction, with long screws & adjustable fences. These vices pull the miters together very tightly, and are particularly handy when you need to compensate for a slight warp
The seller claimed there's no need to use mechanical fasteners after gluing in these vices. OK, they are tight, but I would never assemble a frame without mechanical fasteners.
In may experience, anything from Ledsome is good stuff. As soon as I find a buyer for my huge Pistorius double miter saw & noisy dust collector, I will buy a Ledsome.