Honestly, it's fantastic.
I don't think it is more expensive than the others. They price match with Tesco, so if your order would have been less with Tesco they send you an online voucher for the difference to use next time.
Even if it is a bit more, I think it would be genuinely worth it, it is so rare to get a substitution, but when I used other supermarkets they always had items missing or such rubbish substitutions that you would end up have to do a quick top-up to get those things, which completely defeats the point of doing it online in the first place.
They set up the order 6 days in advance, so eg my regular order is Saturday 8am, and they set it up on a Sunday at 10am, so all the stuff gets put in your virtual basket, so you have first dibs on the stuff, whereas if someone goes on on Friday and orders stuff it might show as out of stock, that's because it's in YOUR basket, haha, hope that makes sense.
I have an annual pass, honestly can't remember how much it is, but it is worth EVERY penny. Then every delivery is free, one each day if you want it, as long as you spend £40. If ever short just add toilet roll/wine and you'll get to £40.