Yes, they’ll work indoors, but they’re not really suited to the role of a general purpose optic nor are they really the best choice for something like clearing a structure. They can’t see through glass, generally have a relatively small FOV compared to something like an RDS, there is some lag/latency with quick movement in a lot of units, most options won’t have a true “1x” image, and they’re really expensive (compared to something like an RDS).
A thermal scope would be a good choice in a low/no light environment where you need to detect living objects that may be camouflaged/concealed, usually with at least some distance between you and a potential target.
ETA: No, that ATN product is absolute bottom of the barrel in the thermal world and ATN is known for absolute shit customer service and generally unreliable products.
If you’re looking for a thermal scope, figure on budgeting $2k-$2.5k at the minimum for a quality budget option. Even then, you’re going to be getting a Chinese core and 320 resolution.