Never ridden any other folder so can't compare, but as an owner of an I4, if all you need is a good, easy to fold, commuter then it's great. The rear rack with Mezzo bag can take a laptop with change of clothes for overnight stay, I've been sent to Manchester, Leeds and a couple of other places with no problem.
If you are fit and your terrain is flat (mine is mainly London) then it is under geared, but I'm about to fit a 48 chainring instead of the 44 and will report back.
Lee