Non transponders aren't a problem per se, but if you have one onboard, it makes our lives a little easier, specially if we are in a position if we have to vector the pax carrying smartie tubes outside the limits of CAS.
Regardless of whether you are transponder equipped or not, you should always call radar units you are planning to pass on your route. It is not only more helpful for us to know where you are and at what height, but may be safer for you depending on whatever else we are talking to.