I suggest you look through earlier threads (there are a few recent ones). My impression so far, based solely off those (I have never bought off FC2) is that:
It might require VPN or even forbid you to watch the content you bought using VPN because to watch it, you need to have a legitimate Japanese non-VPN IP (I don't remember any proof of that, but it's a common practice in Japan nowadays, unfortunately)
You might lose access to the content you bought if the maker decides to leave the platform etc.
A lot of the content there might be found elsewhere, including in standalone DVD releases (essentially as compilations of several clips of the maker)
A lot of the FC2 content is available on streaming sites
So, I would personally avoid buying there unless you know how to bypass the DRM and download the stream of the content you bought onto your device to watch offline. Or maybe use the services of the people who know how to do that (there is another recent thread about that, search for "forward purchasers"). My opinion is that we should not support the system that currently in place on Japanese AV platforms as it's not user friendly, especially towards "outsiders"