Looks interesting and reasonably priced.
https://www.thefirearmblog.com/blog/2021/02/15/grace-optics-m1-topless-reflex-sight/
https://www.grace-optics.com/products/m1?variant=31869686677636
https://www.thefirearmblog.com/blog/2021/02/15/grace-optics-m1-topless-reflex-sight/
https://www.grace-optics.com/products/m1?variant=31869686677636