I *think* that Tropic has larger planes (seating, I would guess, about 15-20?). I only saw small (4-6 seaters) at Maya. Perhaps they have larger ones, but I never saw them.
Personally, to me, it would not be worth the few dollars saved to go over to the Muni airport for all of the hassle. But only you know if it is worth it to you. You do get to see a bit of Belize City, though.