Does this mean you have to 'dial in' each upper kind of like a scope? I've never done so, that would be a learning curve for me.
Thanks for all the responses and sorry to kinda thread jack. I'm in the process of setting up a Trust and trying to figure out what my first purchase for it will be. On the rifle side I'll be doing an SBR + suppressor so just researching what my best options are.
Yes, you dial in each upper.
The block I like is made by SLR Rifleworks. They are very easy to service, and use a detent-based click mechanism to set the gas flow. They work with standard AR15/AR10 gas tubes.
Syrac Ordinance sells a similar one which I've tried, the only drawback when I tried it was it required a straight gas tube, something of a unicorn to find.
Noveske sells the Switchblock which my gunsmith really likes but I tend to prefer low profile blocks that hide under the handguard.
There are also variants which locate the adjustment hex screw on the side; that's a nice feature if a hole in the handguard just happens to line up with the screw.
Then there are the continuously-variable units. Those had problems with the setting wanting to creep as the gun is fired. Most of those now have a second screw that acts like a jam nut preventing the adjustment screw from moving, or they recommend using loctite.
For me, the SLR Rifleworks adjustable blocks have all the features I want and none of the drawbacks I don't. I'm not affiliated with SLR other than as a satisfied customer.