I've had a few problems with the MX-800's particularly when used in houses with Lutron dimmers. I've found that there's a fair amount of tricks and tips involved with debugging these remotes, but nine out of ten times, I can get them working well.

My major beef isn't so much with the MX-800s, but with RF anything. It's just impossible to predict.

My advice is that if the walls are open to go ahead and pull wires for an IR backup. Confucious say "never really on RF to work 100% of time"