Thanks for the feedback. I'm my scenario those deeper burial depths would be very unlikely unless some kind of terrain trap was involved.
I found some more info again: Probes
echoing the 240 size as being a recommended choice.
It seems that an extension piece can be added to the one I was looking at if required (travelling to deeper snow location, conditions). Let's face it, if the burial dept is over 2m, you're in trouble full stop
Advice appreciated but i'm going to stick with my original options.