I've used these tills in primark in many different towns and cities, some stores its not very obvious it's there, but the staff always acknowledge me and sometimes apologise for keeping me waiting until they're free to attend to me (which I always tell them there's no need)
I've never seen them used by anyone else, except once this week when there was another lady in a mobility scooter (though hers was about twice the size of mine!) of course no doubt you will say using the scooter is my choice OP, many people have that attitude that they're only for fat, lazy people. In fact I began using mine as my arms suffer from the same degenerating condition as my legs (funny that) a manual wheelchair is therefore too difficult to push, so I use a scooter. It means I am not likely to shop in primark as it makes my life much easier. My 15 year old daughter is definitely in thier target market, yes even for the homeware, how many adults want a winnie the pooh cushion or a friends bedspread?
I also have twins (didn't really get a choice about that either, only tried for one baby) though at 15 they don't exactly need to go in a pram any more, but I wouldn't begrudge someone using the till to avoid the snake queue if they were using one, I've never seen it happen however in the many times I've been in primark. I would object to being left at the roadside as I couldn't get on the bus home though (which has happened as apparently the baby was sleeping)
What difference does it make to you anyway? If you're jealous of my queuing privilege I would love nothing more than to be able to give you my daily pain, oh and the 40+ tablets a day, and the injections, or does that bit not sound so appealing?