The MFJ-269 suffers from being accidentally switched on when in the box. Newer models have had a switch guard added as standard. I don’t actually like the design of the official MFJ improvement on the 269B as I find it hard to switch on.
My 269 is not the B revision and required improving to ensure it could only be switched on when required. I designed two different guards. One is solid and hides the screw heads, the other looks nicer.
The STL files are available here and on Thingiverse.