The advertising for those mini tanks is terrifying! Just pump them up and go diving with no training required and cheap too. Those snorkel masks with the built in mini tanks look like assisted suicide devices to me! Family to large? Buy them all a snorkel mask with built in mini tank and take them to the beach!
However, there is a place for them if their limitations are understood and not exceeded. I dive solo and am "vintage", meaning I'm pushing seventy years old. My gear is all vintage type but not old. I use a Horse Collar BC and carry my tank in a back pack. My BC has a pouch under the front where I carry a mini tank with a built in regulator. It's out of the way, not heavy and doesn't bump into me. I fill it with an adapter off of my utility tank. (Spare tank for filling the mini tank, blowing off gear, filling motorhome tires, etc)
It's just there for emergencies. An extra five or maybe ten minutes of life. I also carry a RBFK (That's R for really) on my calf, a tourniquet on my BC, all of the standard emergency gear and all of my tanks have J valves. When crap happens, it happens fast. I like to be as ready as possible. Having a few extra breaths sounds like a good idea to me but without the extra weight of a pony tank with an extra regulator flopping around.