It's up to you, but don't forget that with suppliers other than ESB/Electric Ireland you must pay the full bill and get money refunded afterwards. If you get the "free electricity" as a cash payment then you will notice little different other than the hopefully lower charges.
Other electricity providers
If your electricity provider is not Electric Ireland, your Electricity Allowance is paid directly to you to use towards your electricity bill. In this case, the allowance can be paid into your bank account or at your local post office.