Free internet for a bit cannot be bad
Agreed, it can't be bad!!
But only if you use PAYG internet calls. This means instead of paying 0844/0845, you instead pay 0871, which is then refunded.
If you pay a monthly fee, for unmetered internet use, you still pay this monthly fee, but make less use of what you've already paid for. In reality, the main beneficiary of this is your normal ISP, who provides less internet than what would normally be required.
Also, when you send off your bill for the 0871 calls, remember to add on something to take account of your printing, photocopying, and postage costs.