Re: Chey Tac M200 in 375ct or Thor M375
The M200 was developed as a modification of the Windrunner initially, by scaling down the M96 receiver into what became the XM04 receiver. Cheytac modified it in a few areas, particularly the barrel and bipod assembly, but then a falling out happened with EDM. Many of the M200s were built by other manufacturers against EDM's wishes.
Thor is essentially Knesek Guns, a company with a checkered past. Over the last few years EDM has spun off some of its product line to other companies. Nemesis Arms now makes the .308 Windrunner, for example and apparently Thor is making the XM04.
This is where it gets a bit confusing as Knesek is/was a Cheytac dealer, selling M200s. So now they are building XM04s per EDM's specs, but also apparently building an M200 copy. I'm not fully aware of what the situation is, but from what I've heard they are making two different receivers as EDM-spec receiver does not accept Cheytac 7-round mags, but the M200 copy does. It's quite possible that they are selling the rest of EDMs volume of XM04 receivers while manufacturing the Cheytac-spec receivers now.
It's really confusing and honestly, I'd stay away from both. As far as I know, EDM never made a .375 variant, but you can find EDM built XM04 .408s for sale on the various forums (including this one). There are so many better platforms to build a .375 on.