I have, coincidentally, RF3.5 too. (EDIT! It's been so many years!) I got RF2.0 in the early 2000s. I recently bought 9.5 because, through the years, I've lost the 2.0 cds even though i do have the controller.
Just for kicks, just now, I tried using the 2.0 controller on 9.5. I selected it in the Simulation>Select Controller menu. It was listed as a generic USB device. Using the edit button, i was able to select which switches control which features, and assure that the stick inputs were assigned to the correct control surfaces.
It worked, but without that handy reset button, without as many switches, and without the ability to select aircraft, airports, and more from the controller itself.
The 9.5 controller is so much nicer. I really recommend that you get 9.5 with the newer, snazzier, more feature-rich controller.