Ren, if Flysky is the as the Turnigy which I believe it is, the model number allows you do custom profiles, but if all your tank are setup the same way, you don't need a separate model per tank. In theory you should only need one model for all your tanks.
If you turn on multiple tanks and they all respond to you one radio at the same time, then you are not using model switching which means as long as you set up your tanks the same way, you can share model on multiple tanks.