The horror stories you read relate as you say, to what I suspect to be the relatively few cases where something goes wrong. For these poor souls they have to cope with the currently totally.inadequately staffed Plusnet customer services department.
The majority will only suffer a short outage during the change over and all that you need to do is change the hub. I can't comment on whether customer services are any better should things go wrong with other budget providers. I suspect that in general you get what you pay for so if you pay for a premium priced ISP then you will get better service from their customer services.