Interesting article, first I've heard of esims. Two numbers on one sim and cheaper roaming as well, and I think anything that does away with inserting those fiddly fragile sim cards has to be good. Cant think why its taken till now to make electronic sims.
I think that could be misleading advice, as it doesn't sound as though uswitch actually know how they are going to work yet.
You're most likely not going to be able to change networks yourself as you can at the moment, but will need to contact the network to do it. This means that they will actually be more restrictive than physical sims which you can change yourself in seconds.