Having used Icom hand-helds for the last twenty odd years I’ve found they have done everything I need. I get 40nm range to other aircraft and can usually raise London Info from half way between Cap Griz Nez and Lydd.
The most important thing with any radio installation is the antenna. Hopefully the existing antenna set up in your Varieze will have a suitable ground plane. This is more of an issue on composite aircraft than on metal or rag and tube construction.
I seem to recall that there was a problem with RF signal getting in to the mic/audio input to some later Icom hand-helds if a headset adapter / intercom was used. It wasn’t a particular model, just odd units were affected. Hopefully it has been resolved, but possibly worth checking if you buy second hand.