These are new to me and I think the idea is great. Don’t need to pack a separate battery charger, just pop the cap (cap has short elastic lanyard) and plug into USB port. Little led light on the cell goes from red to green when fully charged. The mAh rating, 1200, is less than an alkaline (not sure how it compares to NiCd or NiMH) and the discharge profile is different. That discharge profile is flat with a sudden drop at end, so the cells may not play nice with the battery life indicators on some devices. Ie, your camera may show close to full battery then suddenly empty.
I’ll give them a go and see what’s what.