This conversation is like deja vu to me. When we were there for my friends bachelor party and I suggested Firefly like 3 or 4 people were so opposed to the concept of off strip. Like it was some weird random black hole. The bachelor looked the place up and decided he really wanted to go so it ended all debate and discussion, but had that not happened we wouldn't have gone because if people have already made up their minds that going off strip is a problem, it would have been a problem. We had a blast, everybody found plenty to eat that they liked, the pitchers of mojitos and sangria flowed and the beer nerds had their fill of a solid beer selection. When it came time to settle up for the bill, people were even happier since it was like half of what dinner was the previous night for only like 2/3 of the group.
If the group is fickle enough that waiting a few minutes for a cab after dinner will somehow kill the mood then I would avoid. To be honest with you the wait beforehand is probably the bigger risk since Firefly is a crazy popular place. Pretty much a nonstop stream of cabs and ubers dropping off and picking up. The place has to just print money. I dont remember if they take reservations or not so that is probably worth a call to find out. IIRC we went fairly early since everybody had been up since pretty early in the morning due to the time change and it being the first day.