I love conversion kits. I've got two Colt Aces (one for the Series 70 and the other for the Series 80) with the Williams floating chamber as well as the Kadet Conversion for the CZ-75.
Never played with the Ceiner for the AR and instead bought a Kuehl dedicated upper with the modified Ceiner.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!