ok came across autotrader fuel saver while looking on the net and says 5.99 a month but when i look it says if you spend 50 or 100 pound in ther online shops you get a 5 or 10 pound petrol voucher for asda teso or sainsburys

anyone used this or think its worth it was thinking i spend over a 100 pound a week on shopping in asda so tht would give me 4 10 pound petrol vouchers o0 i think if anyone has herd or uses this please let me know what they think???