Always err on the side of caution. My rule is if at least two people tell me it will be disastrous, then I would rather not risk the life/well being of the fish.No offense.. But this is one of the reasons why it is so frustrating for beginners.
Half of the people say that labs/dems are a proven combination and would be fine and others say that the dems will wipe out the labs.. How do I know what works for sure.
Another rule is that anything in the Pseudotropheus is going to be a mean fish. It will rule the tank. This is something I have been told by nearly every mbuna keeper I've met (that includes researchers and hobby keepers).
More peaceful mbuna are the Labidochromis and Labeotropheus genera.