Just find the number of the local office and ask them if you can talk with their instructor for 15 minutes. My office was always nice about doing this. I've heard that some offices aren't (which would make me wonder what they're hiding).
About the December test, realize that you'll be applying very very late in the cycle, which will put you at a serious disadvantage. It may be worth considering waiting until next year to apply. (Especially if you're not happy with your practice tests by Dec.)
10-4 on the late part EC. I registered at first to take the test in Oct but then changed the date since I knew that finishing my UG degree (in 6 weeks) plus studying for the LSAT prob wouldn't be a good idea. I'll be finished in mid-October and decided to dedicate my full time to prep for a couple months. I doubt seriously I'd have the credentials to get into a T14 school anyways but on the chance that I can score high, then feel I'd fare pretty well in the admissions process.
BTW, if the instructor would talk to me, what's important? Experience? expertise? dedication?