My LMB will eat anything...he eats all algae, he eats the flakes I feed my clowns, he eats pellets, he eats frozen meat (guess he likes meat as well).
I haven't found anything mine won't eat, and he is getting a decent belly because he never stops eating.
I bought one from this site. Initially it would only peck on the rocks of my tank. Eventually it started to eat the seaweed selects that I feed daily. Eventually it started to eat everything (as darknes stated).
Like with all fish their can be exceptions about how hard they are to keep because I have noticed some people posting problems with them. But they are usually pretty easy, mine has proven to be very easy to feed, eats everything including meaty things. If he is going in a 29 gal. pick tankmates appropriatly, mine is quite the bully with other rock dwellers I have tried to introduce into my 20 gal. He killed a royal gramma within 3 days and harassed a gobie into commiting a suicide jump out of the tank. He gets along great with my 2 clowns and shrimp. Keeps alage under great controll also.
I think you would be fine with one. Mine just don't like to share his rock work with anyone, but he has been in there the longest also and think he owns the tank. Yours would be added last. I wonder if any of the other blennys would do as good of a job with the alage controll. I just think the LMB is kinda plain looking but in a cute way of coarse.
LMBs from what I have seen only eat the diatoms off the glass and rocks. Out of the two I have had they will not touch the hair algae I got them for in the first place. Eventually they adapted to eating the flake food I put in for my clown and goby and quit eating even the diatoms.
My lawnmower would eat only diatoms or other microalgae growing on the live rocks. I've been trying to wean him onto algae sheet, but no luck so far....As long as you have a plenty of live rocks in your tank, you should be fine.