Got an S 35 the stand alone gunsight and it's an impressive upgrade from the 300something Bering hogster I have sensor wise. All the Steiners thermals share a similar design. The Steiner is pretty techy with lots of features wifi, video, heated seats, I think you loose some of the techy shit when you move to clip on. These Steiner thermals are literally the size, shape and weight of a smallish brick with a battery pack on the side. I got a hella deal on it with a pretty big factory rebate and the 640 sensor is outstanding visual image is nice. It seems to be made of metal and although you should not use it in a blacksmith's shop I think you could beat someone to death with it remount it and it would work.
Since you are new to thermal I'll add this opnion Clipons can be kinda a niche item especially since this one needs an eye piece to be used as a handheld scanner and the eye piece seems to be out of stock alot. You end up doing shit with your night gear that you didnt envision. You are putting a 2 pound brick out, maybe way out on your rail and have to shoulder or at least get behind your scoped rifle and point it at everything you want to look at. If you are mostly stationary or shooting from tripods this isnt much of a problem but it can become an annoyance and usually results in buying a handheld thermal scanner I use NODs to help scan picking up movement then going to the gun as my ranges are shorter 200ish yards max.
General consensus is this is a contracted China made unit with a Steiner nameplate so dont think you are buying an American or German product.
Warrany period is a short 2 years.
Bering is at least 3 years
AGM has some stuff with 5 years
All that being said I like the S-35 over my Bering due to the sensor, image and techy shit.