The Green Efests tested well according to Mooch, and they've not given me any problems for the past year or so. Different makes can vary quite a lot in size - the Keepowers are tall & thin, the Green Efests are shorter & thicker. 2x Purple Efests in the VCM Stacked and you'll not get the button screwed in properly - greens fit fine. Seems a bit random; but it's helpful when a vendor lists the sizes - otherwise you can get caught out. If you Google them you can usually find someone who's posted the specs somewhere...