Chris,
Just to clarify one aspect, the pilot would not, infact, switch off the transponder - ATC will filter it out and not display your data to avoid "clutter".
You will still be "squawking" (pardon the expression) so that TCAS still functions (notwithstanding the limitations you mention above)
So, buy the kit so you show up on radar, then we'll filter you out so that you don't again...