If you need a free, open-source alternative, is the undisputed king. It supports FTP, SFTP, and FTPS. While its interface is a bit dated and it doesn't support FXP transfers out-of-the-box like FlashFXP does, it handles 95% of what the average user needs—and it’s completely free and safe.
: Some software, including FlashFXP, offers free trials. This can be a good way to evaluate the software before deciding to purchase. However, free trials usually have limitations and expire after a certain period.