Mode S
The Honeywell plug-in replacement for your current transponder is the KT73, not the 70/71. Only the KT73 meets European Mode S requirements with flight ID.
It'd still be cheaper to put in a Garmin GTX330 even though there is more labour invoplvd to change tray and connector. Thr Garmin has push-button entry and some other useful features - flight timetr and audible altitude alerter.