The only switch I use is a MFJ-1704. I use it to switch between antennas though. The port to port isolation is supposed to be 60 db and that is more than enough to protect the front end of the unused rig.
I would make sure the unused port is grounded on whatever switch you buy. Most do but some cheaper ones may not. I would even look on the manufacturer's website and download the manual first. Go with the one that has the highest port to port isolation.
Using the switch with one antenna and multiple radios scares me. Shit happens and mechanical things can fail. It's not a big deal if you knock out a cheap CB set but I won't take the chance with something expensive.
Inspect the internal solder connections. I have that same switch. One of the copper strips came loose. It was barely soldered to the center pin. I went ahead and touched everything up.