IMHO, the trigger guard safety sucks regardless of which hand you use. The tang mounted safety is right there and can be used by lefties and righties alike. You just slide your thumb up. Plus, you just have to glance down to see if its engaged or not, without having to look sideways at the trigger guard.

I had one on my Browning BPS when I was a kid, and one on my my Mossy 590. Its not too different than the three position safety on my Ruger M77. For that matter my RWS has one too. Heck, even the AR safety can be used by a lefty. You just use the trigger finger rather than the thumb. A trigger guard safety is, in my opinion, a PITA. And like you, I leave it off on my current Maverick bedside shotty. As far as as I am concerned the gun has no safety. Its an empty chamber and once racked its a matter of keeping your finger off the bang switch. I really would prefer the top mounted safety though.
FQ13
PS As far as the forends, they are ambi. Just like the AR only in reverse. If you are RH, you trigger them with your thumb. LH, use your index finger.