I've gone to Allen's drop-in adult gymnastics classes three times and have had a great time! I've never done gymnastics before and the skill level of the attendees are beginner to int/advanced.
The class structure involves trampolines, tumbling, and some fitness (with some pretty creative and fun exercises). Allen and everyone else are very friendly and keen on offering a hand or giving advice on skills.
It's an unbeatable price for an hour of instruction and an hour of open gym ($20 the first time, $15 thereafter). I believe he teaches the gymnastics class Mondays and Fridays. Highly recommend!