I have a small Insingo and small 21. I find the Insingo to be more handy overall because things will slip off the curved part of the 21 easy (like with any curved blade like that), and the curve becomes drastic an inch from the tip, meaning about 2" worth of blade is used in many slicing tasks. The Insingo has the full ~3" blade for use in the same tasks. (Since I have the smalls, I can't say if this difference matters as much at the large size, but at this size, the difference is significant.)
For puncturing tasks, however, the 21 wins hands down. It's not overly difficult to puncture with the Insingo because the tip is still pretty small, but the 21's is more acute, and the Insingo's width from spine to blade gets thicker more quickly than the 21, which also makes puncturing tasks more difficult with it.
One thing I didn't realize until I had both in my hands is the thumb stud is set further away from the handle when closed with the Insingo, making the Insingo easier to open. It's a matter of ~2mm (on the smalls at least), so it's not a huge difference, but it is one that can be felt. I wouldn't buy an Insingo over a standard 21 only because it's slightly easier to open, but it's an added bonus.
I've only had the small 21 about two weeks, so maybe my opinion will change, but right now the Insingo is superior for what I do every day.
edit: Rereading your post, I want to also mention the Insingo excels at food prep. I use mine all the time.
