The biggest cost of living alone is getting on the housing ladder. Even with a large deposit saved up, on my fairly average UK salary, the amount I can borrow on a mortgage does not get me very far in my area. If I had a partner, even if they were on a minimum wage job, it would change what I could afford from 2 bed terrace to decent 3 bed semi-detached.
Not saying it's unfair, just that it kind of sucks.
I've been thinking about this ever since my closest supermarket got the same app system.
Anti-theft seems to be done by random audits of scanning 3-4 items. I've had this 3 times out of the 20 or so times I've used it.
In that regard, it seems more risky to try any funny business with it. With the traditional self scans, cameras aside, it's quite easy to fool them, and they are reliable and predictable machines. I'm sure it would be easy to slip something at the bottom of your bag, but if you get caught on an audit, I'm sure it sets a flag to audit you more often.
The scan-at-end checkouts can be used without identity, where as the scan-as-you go, at least for my supermarket, you have to log into an account linked to your identity before it's used. This may deter a lot of casual theft.
I don't use any third party sign in services. Email is the only option. Any third pary (Twitter, Google, Facebook, Github) etc can stop your account, making you lose access to anything you signed in via their account.