I don't have a lot of experience with thermals
and for sure not any clip on's
But I have used a bunch of different high powered led lights designed to be added to a rifle that you can then shoot 200+ yards and ID targets pretty well, as they hold light in tighter patterns and have colors that don't make a lot of if any shadow, so they don't spook most wildlife when you light them up
there designed for hunting at night!
again NOT any where near what a thermal will do, or how they work,
but maybe there legal and would work for you! and save you a lot of MONEY in the process!
do soem online searching for them and your sure to find a lot these days
I won';t bother listing any, as I am not sure they even interest you!
but could name a few if needed!
you will find way more info about these things IMO< on more varmint/hog hunting dedicated forums too!
just so you know,this as well!