I voted for the Bushnell TRS-25, which I have owned for a few years.
I bought it from Amazon for less then $80.
It gets great reviews and has stood up very well on my Colt M4.
It still has the original battery and is still running fine, given that I haven't really had it on all that much.
BUT **********
My older TRS has the Bushnell name on the side in a gold-tan color lettering.
The new TRS has the lettering in White.
Apparently the new TRS is NOT as good as the older version.
Buyers report that if you move your head, as the dot approaches the side of the tube, the dot just disappears. So you have to keep your head in just the right position and not move or the dot will disappear.
The old TRS LED lamp is mounted at the 4:00 O'clock position in the rear of the tube.
Apparently the new White letter version moved the lamp to the 6:00 O'clock position.
For some reason this may be why the dot disappears if you move your head.
With the old version you can move your head as much as you want and the dot stays visible until you move your head off the rifle.
NOTE that Bushnell may have fixed this problem on the latest White lettered vesion.
If you look on the Amazon page and look down to the "Often bought with" list, you'll find several inexpensive mounts for the TRS.
I bought the medium size and it gave me the desired absolute witness.
These mounts are cheap, but it works and that's about all you can ask.
It might not be up to heavy combat, but then I doubt the TRS is either.
For what I wanted the TRS and the mount work as well as I could ask.
On the Amazon page the LED lamp position is discussed about being visible in the lower right side of the tube on the White letter old version.
It's not distracting and I noticed an oddity...... If I position the sight forward on the M4 rail I notice the small lump of the lamp.
If I position the sight on the rear of the receiver rail I don't see the lump of the LED.