I've tried to root Nepenthes inermis cuttings a few times without any success, mostly in live sphagnum. On a list of difficult cuttings to strike, N. inermis is definitely up there. Anecdotally, I get the best strike rate in my regular mix of sphagnum and perlite or live sphagnum (generally 80-90%); the water method and the perlite method were comparable for me (60-70%), although rooting seems to take longest in water.