IMR batteries are often referred to as "safe chemistry" batteries as they are a different chemical composition to standard Li-Ion batteries, with lower internal resistance, and should be able to deliver a higher current while maintaining their capacity and avoiding thermal build up.
I had bought some efest imr ones but both my kits came supplied with icr..
so i take it that icr are cheaper and after some reading one is cobolt (icr) and manganese (imr) not so of the differences but i was just curious
Both are ok to use, but find out if your device needs a protected or unprotected batteries.