It is not a one-time free trial that ends after two weeks. The two-week free trials on the standalone version are per product and recycle after six months... meaning you can try the F-16C for two weeks and then try the F/A-18C for two-weeks. Once the two-week trial for an specific, individual module has expired, you can't trial it again for six months... so once you've tried the F-16 for two weeks you'd have to wait six months before you could trial that particular aircraft again for free.

The full fidelity modules are very deeply modeled and will require a great deal of study and practice to learn... so only purchasing one at first is not the end of the world... in fact it may be more to your benefit to limit your focus to just one aircraft/helicopter at a time.

Beyond that the Flaming Cliffs 3 (FC3) aircraft pack is a pretty good bang for the buck, especially when it's on sale like it is now ($24.99). You get several aircraft at once for a pretty good price. Just note that none of the aircraft included are full fidelity (so not the same depth of systems modeling) nor do that have clickable cockpits. Their flight models are still top-notch, but the systems and avionics are simplified a bit, so the learning curve is not nearly as steep as a full fidelity module. A lot of folks will tell you to skip the FC3 planes and pick the full fidelity aircraft that really piques your interest. This isn't bad advice, but I think it's worth giving them a trial sometime anyway as I still find many of them to be a great deal of fun for the money.