For serious use......for that price? Nothing.
Get a XS tritium Big Dot or for slugs, the Express sight/Ghost Ring option. Fast and accurate.
If you actually intended to spend money on a serious optic, an Aimpoint Micro H-1 in a low mount would work well.
"And Shepherds we shall be. For thee, my Lord for thee. Power hath descended forth from thy hand, that our feet may swiftly carry out thy command. So we shall flow a river forth to thee and teeming with souls shall it ever be. In nomine Patris, et fili, et Spiritus Sancti. Amen."