After hardshell kayaking for 20 years I picked up a couple of duckies last year. My back and hips just couldn't take being locked into a kayak anymore and a duckie is more comfortable. Also I wanted to do more self-supported trips and they are easier in an IK.
So my experience is limited. The only boat that I've attempted to roll is my Force Expedition. 1. It ain't easy. I could hand roll my hardshell but it took a lot of work to roll the IK - and occassionally I still miss or fall out in the process. The only reliable way for me to do it is with an extended paddle roll. It's not my preference but that's what it takes.
I don't have enough experience to say if an IK roll is useful or simply a trick. I've only done a combat roll a couple of times, but I can say it was a much more enjoyable experience than swimming. I HATE
swimming. I got throttled in one violent rapid last year and there was no such thing as hanging onto the boat. Personally, if I'm going to run some continuous IV I sure feel better having the option of rolling. Maybe with more experience I'll give it up and just try and hop back in but I don't think so.
Note: I've seen an open canoe hand-rolled, both sides, so we're all nothing but wimps if we can't roll a lil ole IK