Hi Nipper
the Becker and Funkwerk (ex-Filser) are both good 57mm panel mount instruments, and easy to install. The Becker can have a 'dongle' encoder which minimises its wiring; the Funkwerk has a built in encoder so is even easier (2 wires, + volts and ground with a supplied wired connector/code unit, and static presure).
The certification standard requires the 24bit code to be 'fixed to the airframe' (the wording is longer and more convoluted, but means effectively that). The Becker has another dongle you chain to the aircraft and unplug if you change the set; the Funkwerk has a bit of Flash Memory in the plug at the back.
Funkwerk is a bit smaller and lighter, and currently more cost effective (once the AD business is sorted out). I suspect to keep market share it will stay that way. Also, UK dealers have stock, Becker is longer delivery - not a problem if you plan ahead.
Interesting that the CAA seem to want to insist on an extra requirement (air/ground switching) not required in the rest of Europe. Remind me why we all come under a common EASA system?