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.
I have a Ledsome Miter Vise. It is a well designed and well made piece of machinery.
Of all the choices I have in joining tools it is probably the one I use least, and I have a lot of options.
I don't mean this to reflect poorly on the tool. It might be that I just haven't spent enough time to learn it properly. I never integrated it into the routine of my shop.
I do know that it can exert more direct pressure on the glue joint than any other clamp or vise I have used, including the Masterclamp.
It might be the perfect tool for some, but I would suggest actually trying one out before purchasing.