Make sure you read the small print, when you fill up they take £100 deposit from your bank it sits there on hold until the money for the fuel comes out. It then un-holds and comes available again.
Have a 1000 nectar point offer but how much is the minimum spend. I used to buy BP fuel which is great when the local petrol station was competitive on price with supermarkets but they abandoned price matching some time ago. Car always seemed to run a bit better with BP fuel although nowadays I use Tesco high octane momentum which seems as good.
There is nothing for free, you disclose your personal data plus you're asked to fuel your car so I wouldn't call it FREE
Where I live BP fuel is 10p per litre more than Tesco which is 400 yards further up the road, so to fill my car would cost £6 more than Tesco.. so how much are 500 points worth?