This is just the flip up.
If you only need the flip mount, it is part number 200251. Aimpoint calls this height 39mm. 39mm optical center to top of rail.
https://www.opticsplanet.com/aimpoint-flip-to-side-mount-for-3x-mag.html
-Aimpoint
Yes. This Aimpoint Flip to Side Mount for 3X MAG was specifically designed for the 3x magnifier and other magnifiers with a 30mm tube including the 6x Aimpoint magnifier.
I recommend using the Aimpoint Flip to Side Mount for 3X MAG MPN: 200251 for that set up.
You would want the taller model: AI-RMT-SKA1-1-200251
The lower height would be the one you need: AI-RMT-SKA1-1-200250
If you are using the spacer, you want the tall one. If you are not using the spacer, you would want the shorter one.
AI-RMT-SKA1-1-200250 You would want the 38.5mm, yes you can use most 30mm magnifiers.
It depends on what height the optical axis is with your mount set up. If the red dot has a 30mm optical axis you would need MPN: 200250, if the red dot has a 39mm optical axis you would need MPN: 200251.
You would need MPN: 200251.