Used Tesco for almost a year now and only go into the shop very rarely. Only had one bad experience where they never showed up on the night we were entertaining and had nothing for guests to eat/drink.
I find it better as I can shop at my leisure over the course of the week, and spend less than I would in the shop as there is none of the ‘Oooo.. that looks nice, chuck it in the trolley’. Probably save a good £20-£30 a week, even after the delivery charge. Our substitutions have been ok on the whole, and the price match is good so that if they sub a more expensive item you still only pay for what you actually ordered. Only weird substitution we ever had was a pack on Naan bread instead of a packet of couscous…. no idea where that came from.