My grand-daughter, who lives in Edinburgh, has bought one of these and loves it. However, she is young, and strong, and fit, and seeks out opportunities for intense exercise.
I'm 66 and averagely fit. It's hilly round here too. My MTB has a low gear of 26" and I need every one of those inches every time I go for a ride. MTB with slicks is the way to go. Probably cheapest option as well.
In answer to the second question: yes, a lot of dealers have sold out of affordable bikes, and they are hard to find on the secondhand market as well. No doubt the market will correct itself before too long, but at the moment getting a reasonable bike is quite a challenge. I know; I've tried.