The M21 seems to get a bad reputation. In reality it's one main weakness is shooting from dark areas into very bright. With the newer versions they have a bullseye reticle which looks a lot like the Eotech and has a 1 moa dot in the middle. Shooting a Tavor off hand with this site was quick and surprisingly accurate.
I also use them on firearms that have charging handles on the side which make the Eotech a poor option. The quick release model with the new reticle is actually not bad at all. I'm actually glad the Tavor came with this. Even if I didn't use it for the Tavor it sure works great on my non restricted 9mm CX4 Storm.