Icr are cobalt, higher mah, available with protection circuitry.
imr are manganese, no protection circuitry option, can drive quite high current safely.
For boost vv, single battery, pv, like the Provari or lavatube, imr is key. For buck vv, two batteries, including all notcigs products, icr is also fine. The notcigs pv have current limiting electronics, short circuit protection, and a diode "fuse" that will pop if it goes too high.