I don't have a big bushy mountainman beard, but I do have one and I dive the G. Diver with no issues. My brother-in-law has said big bushy moutainman beard and dives one as well and has no issues at all. If you have an opportunity, go try one out before you buy. It's a pretty expensive investment and I'd hate for you to not enjoy it after buying it. It's honestly all I dive if I can help it and I don't see myself going back to a conventional mask & reg unless I need to. But they can feel a bit cumbersome at first and it does take some getting used to.
If you decide to pick one up, do yourself a favor and get a few things to go with it:
1. QD hose & fitting. They don't need to be the Ocean Reef ones because those are quite expensive. My hose is a MiFlex 40" and I think an XS Scuba QD fitting.
2. Ball swivel - you can see mine in my avatar as it lets my route my primary hose under my arm for better streamlining and less chance of getting hung up on anything
3. Surface Air Valve (SAV) - so you're not breathing down your tank on the surface
And then I've also added the adjustable directional exhaust valve and may add the Space Extender kit later, along with the coms unit.