The torx and allen keys are different. The allen key is hexagonal, with straight sides. The torx bit is like a star with curvy in sides. The T50 will fit exactly right while the allen key will have to be forced, and it will end up wearing the bolt and making it REALLY difficult to remove.
You can undo a phillips head screw with a flat blade screwdriver, but it will work better with the correct phillips screwdriver. It is sort of the same thing with torx and allen. Both allen keys and torx bits are available as either stand alone tools or sockets. There are quite a few torx bolts on the RIII so it is worthwhile investing in a set or two.