I thought I was going to need to order once per month but a 3-pack is are lasting me almost 3 months using two diffusers. I love that you offer this because I never remember to get around to it in enough time before everything ran out. I just added it into my budget and put it on auto-pilot and now it’s like a surprise I’ve given to myself when it arrives. If you had a way to ‘randomize’ the selection that would be awesome.