A bit of a nightmare
The offer and cashback seem good value but I had major problems.
Initially all went well, the Wifi router was delivered quickly and the Openreach engineer arriving as promised to install a new line, but then the problems started.
TalkTalk promised to activate my service 25/7 but this did not happen until 27/9 though not fault of my own, and in the meantime my cashback was rejected. I had to raise a claim on Quidco and complain to the TalkTalk CEO office to get the service sorted and help getting the cashback paid.
My advice is don't make a decision based on the amount of cashback as this may never be paid if TalkTalk has issues outside your control.
TalkTalk customer service is outside the UK and whilst polite it seems unable to do much apart from escalate, but then nothing happens. On a more positive note the broadband performance seems good so far with speeds in excess of 70mbps at peak times.