AR scope mounts took me a little while to figure out at first too.
In general, I like the one piece mounts best for two reasons.
The AR top rail ends just before where a standard ring typically needs to go when mounting a typical scope like a 2-7x33 or 3-9x40.
A one piece mount cantilevers the rings forward enough to get the proper eye relief.
Also, the sight height above bore ( ~2.65" ) is higher than on most bolt action rifles (~1.5"). This requires special rings or risers. The one piece AR mounts typically have the correct height out of the box.
Here is an example
one piece that works well and is fairly inexpensive
, but a little heavy.
Your red dot will probably not require the same eye relief, but a one piece mount is sturdy and keeps your options open.