The handset of the EQ5 dual axis set will work for me too! Just tried out a mate's handset and it works just fine with my EQ3. Same handset works with both mounts.
Thought I'd add a bit more info about this handset, even if only as reference for other users. I'm going to describe the difference between the two handsets, and how to adjust the RA drive rate in the handset if you find your RA is running fast or slow.
The ONLY difference between the handsets is rate of the RA drive coming of the handset is a little faster in the EQ5 than that of the EQ3. If you use the handset from an EQ5 on an EQ3, you will need to adjust the RA rate, or the RA will be running a bit faster on your EQ3.
Now, regardless if your mount is an EQ3 or EQ5, you can adjust the RA rate by tweaking the variable resistor inside the handset. To do so means opening the handset. You will need to pop off the four buttons on the front panel along with the various screws. The variable resistor is located on the left of the North/South/on-off button on the top left hand side. The pic below shows it location. The handset will work while open. With a fine screwdriver, make the adjustments with TINY turns of the resistor while using high magnification and a defocused bright star. Also use a star close to the celestial equator as these will be moving further than stars close to the celestial poles. This will show rate changes very quickly. Low magnification is not good enough. Once the necessary adjustment has been done, close up the handset, replace the screws and the buttons.
