Today, somebody asked about this S4’s capability to make proper positive contact with a flat-top 21700…perhaps also to other flat-tops. Remember when even the SkyRC MC3000 had contact issues with flat-tops too? Yes, this Vapcell S4 does make positive contact with the 21700, and all my other flat-tops. See why in the photos below: (edit: I just checked, my Miboxer cannot also make contact with my 26650 flat-tops too!)
SkyRC MC3000 left, Miboxer C4-12, Vapcell S4+ right:
The Samsung 21700 inside the bay still has plenty of room to spare, up to 75mm.