A lot of confusion here, as to the differences, and general similarities, of the two sports. I suggest reading the rule book(s), and attending some well-run matches.
There is some valuable info in the previous posts.
You can shoot one IDPA match without being an IDPA member. Unlike USPSA, IDPA does not collect any fees from shooters, so the only revenues are membership dues.
Concealment garments are not always required; some clubs will dispense with them in hot weather, or will require them only for sanctioned matches.
The test in IDPA is execution; the creativity is in the mind of the CoF designer, not the shooter. Targets must be engaged in a specific order, depending on how they are presented to the shooter. If you are shooting over a barrier ("cover"), the targets are engaged near-to-far, if you are shooting around something, they are engaged outside-in.
Spent mags must be retained if there's a round in the chamber, regardless of whether there are rounds in the mag. Such reloads are supposed to be done off the clock, and not "under fire". The standard reload in IDPA is from slidelock.
I officiated a USPSA Area championship two weeks ago, and a state IDPA championship last weekend, and saw shooters DQ'd from both; I've seen little difference in the safety aspect of the two sports, as the safety rules are very similar, and can actually be more stringent in IDPA. If matches appear to be unsafe, then look for a club that adheres to the rules.
A constant in both games, surprisingly enough, is that you will get penalties for varying from the CoF requirements, or the rules!
