French rules say you must have a transponder to enter class D. This makes visiting France a pain with no transponder. This rule is not well enforced, but if you get ramp checked…
The Dutch will not allow you above 1200 ft without one and there are also TMZ’s.
TMZ’s in the UK are becoming more common and a mode s is the best solution.
I have a pcas unit which will see you coming so you might live longer.
Cons apart from the cost are the weight – the Trig TT21 is probably your best bet. You can fit the unit yourself (I have fitted several for friends with no issues.)
It is likely to become easy to do ADS-b out in a few weeks and I suspect that over the next few years this will become a big benefit.
Rod1
Trig TT31 mode S with ADS-b ready to go…