Couldn't I just continue to pay by direct debit? My landlord doesn't want me to switch anyway, so I won't unless I'm forced to. However, if I am forced to switch, that sounds like a major disadvantage. At the moment I pay by direct debit. The amount is fairly accurate for electricity, but less so for gas, which varies according to the season.
I check the readings regularly and always make sure that I'm in credit, which means I sometimes receive a refund, but I could choose to pay an average amount over the year, so that it balances out. I'd be highly miffed if I had to go out in the snow and ice to top up or keep my heating down at a time when I need it most.
(Hope that makes sense.)