i've been lucky so far to not have experienced strips failing to work. Touch wood. I got lucky and dodged the bad batch a few years ago, and might also be lucky re apiary location and proximity of beekeepers constantly exposing varroa to low (sub-lethal?) doses. Only strips I have used are bayvarol, apivar, and apitraz. I had a less successful experience with a gel treatment, i think it was apilife var a few years back, salvaged with strips.
I think this year is the year I finally trial oxalic/glycerine strips as an early autumn treatment - the hard work figuring out mix and medium has been done by a number of people, i do feel like a bit of a freeloader on this front.. many of us here we