So far I haven't had any problems with my purple 4200 mah efest's working, there the same size as the 3500mah purples as well. The 4200 mah green is a little shorter but all fit fine and don't give me any pause about using them. I wonder if the worry about 26650 sizes started with the Mikevapes video? I worried about it after seeing that video but installing and removing the little longer ones have been easy peasy, maybe he had an early production sample?
I tried a purple efest at a local vape shop, and could see it was pushing the battery door out when trying to close it, didn't want to ruin the stout or the battery as hadn't paid for it, so didn't try to force it, maybe slight differences in production as they are only meant to be 1mm to long, such a small amount.