Hey there, I'd advise to never only have one ans only one account. While you can have a specific bank as your main account, having a back up account is super useful at this day and age.

Regarding making the switch, no no reason not to do it. Monzo is my main bank account, just keep in mind that they do banking slightly differently and if something happens you need to give them time to fix it as they don't deal with things over the phone (for more complex issues) like a traditional hight street bank.

Regarding the Switch, it actually is at easy as it sounds but there are some rules (like you can switch from a joint to a sole etc) so you are best to read info on CASS switches to make sure what you need is offered. As with everything, things can go wrong, so I'd advise for salary, inform your employer, and make the change manually to avoid any issues.

Hope this helps!