>> Carb Balancing Issues
Not really an issue - buy a carb balancing kit, about £35. The process is very simple and only needs to be done once a year or so. After the first time I found that very little (if any) adjustment was required at later checks.
I would agree that for a permit aircraft the carb version is more practical from a maintenance POV.
>> Carb rubber mounting splitting
Again not a major issue if regularly checked (at 100 hour service) not difficult to replace but they are relatively expensive - if I remember rightly about £120. the pair BUT I would not expect to have to replace them more often than every 3 - 4 years, so not exactly a major expense concern and would definitely be less than the extra costof 3rd party mintenance for the fuel injection system.
Hope this helps