I used to work for npower so this is my advice, anyone asking for a prepayment meter is usually (and there are exceptions) bad at managing money or they owe money and the best way to pay it back is through a prepayment meter ie it forces them to pay it back.
It means their priority becomes paying for electric as if they don't they have no lights/tv/shower/kettle/washing machine etc etc
It isn't something someone usually requests, it could be that they haven't paid their bill and the electricity supplier wants to put a meter in.
The meter belongs to the local electricity company and they won't change it back to a credit meter because you ask them to, you are not the one who will be paying the bill as they know it is a tennanted property from their credit check questions when someone moves in.
The prepayment meter can cause problems with it just costing more per unit and standing charge, it can put potential tenants off, finding that you have miscalculated how much money you needed for the weekend and trying to find somewhere open on a sunday night to top up the supply can be problematic. If you are ill your electric would cut off if you haven't been out to top up etc etc
My advice is to think before consenting. If the electricity company want it fitted then you have no choice (I used to sort out the warrants for breaking into people's houses who refused us access to the meter to change it)
There are better ways to budget such as paying monthly either cash or Direct Debit.