I nave no experience with it, but it does look very similar to what I ended up piecing together. Specifically, I do like having a flexible but supporting nylon backplate.
I did the whole "DIY SM harness" and the issue I had was I eventually wanted a soft backplate for some additional support, and ended up using a "Mares XR Soft Back-Plate." While DIY is definitely possible for a new SM diver, there may be additional frustration in getting it right, and you might end up doing a lot of swapping things around until you do get it right. (speaking of which, I should probably sell the hardware I'm not using, including those plates)
The OMS looks somewhat similar to what I ended up with, and I think it should be just fine. I'm sure some of the popular ones are much better, but as you mentioned, twice the price. If I rewound the clock, back to no experience with SM, I might have advised myself to skip the DIY, and go with the Sidestream, even though I really like doing the DIY stuff. You'll have something that works fairly well out of the box, and can worry about making adjustments, tweaks, DIY, etc later.