They'll basically transmit at the same rate. They turn on with gas pressure. The problem is you've got to dump the gas pressure and leave them for a while so they turn off, then back on again, hoping that you miss the other one's transmissions.If you turn on 2 greys one after the other they won't be clashing they never will, right?
Or just buy a yellow (expensive) Shearwater one and a grey (cheap) Aqualung one.
This is what I did for my rebreather pressure sensors; cost me another £100/€120/$140, but I have never had problems. I know of other people that didn't and bought the same colour and they do occasionally have problems.
Do keep a couple of spare CR123 batteries handy. They're hard to source except by intarwebs and they will expire at the wrong time.