well, what do you think would be easier to do? tell "over 150 users" to mess with their connections or configure one ftpd to allow both PORT
and PASV connections?
and besides, there is no "switching" that "would create a lot of problems", you just have to properly configure your system to allow both types of connections. users who used PORT will contiue to use it without problems, and in addition uses who must use PASV becuase of their firewall will also be able to connect.
FlashFXP can connect to same servers as CuteFTP. it doesn't matter what client they use. it's matter how that client is configured.