I would echo the comments above about the utility of a transponder. IMO it does make a difference when getting clearances through CAS and, more importantly, it allows a significant set of other aircraft to become aware of your presence. ATC can also see you and advise conflicting traffic of your whereabouts, even if you are not talking to them.
Yes, it’s a significant investment but like a parachute, there are situations where it’s priceless.
Doesn’t cost much more to add something like PilotAware Rosetta and a tablet/phone running a nav app, which gives you nearly all the possible functionality.