"Using an OS with multitasking support seems nice and simplifies the programming"

NO, it does not. It makes very complex tasks possible and provides drivers for most I/O.

I use multitasking when absolutely needed, it makes a debugging nightmare, but sometimes you have to take the bad with the good.

Another issue is - make sure you get an os that can handle priority inversion or you will get stuck for days trying to figure out what is going on.

A nice non-multitasking OS can make the time to market a bit earlier IF YOU KNOW IT BY EXPERIENCE, else it will take you longer than doing without- of course the time spent comes back next time you develop with it.

Erik