They're basically as strong as the method you use to mount them, the strength of the plastic is incredible, as long as the headers you plug them into are securely mounted to the board I wouldn't worry about them being fragile in the slightest, if you're talking about soldering the ribbon directly to copper traces on a PCB that is not a good idea for durability at all if that's what you're worried about. So definitely use properly soldered connectors and just plug it in.
I2C is just going to require a re-write of your communication code, a one time deal, the hard part will be learning the displays protocol, it's documented in the PDF that's on your link so it'd just be a matter of writing the code, only slightly more involved than the display you're currently using.