never played a matte mainland myself so cant compare - I do however had a mahogany gloss concert. Tested with loads and load of strings. I settled on Martin Flouros on this uke - it is loud, and those strings chime like a bell on it.
I do not think the finish affects the sound at all (or at least that I can hear). Looks are personal preference....I prefer gloss. I bought a Classic Mahogany Tenor with a gloss finish a couple of weeks ago and I love it. I was out at the shop and I played a couple different models. I could not tell any difference in sound between matte and gloss finishes just a difference in sound with the various woods.