I have been using Tesco online grocery orders almost very week for the last 2 years or so and almost without exception, they have delivered to time, with 99% order/line fill. Occasionally, if they don't have an item, mostly I don't allow substitutions - firstly because of specific dietary requirements and secondly (mainly the reason they don't get 5 stars), because their pickers choose sometimes very inappropriate substitutes. It's not however restricted to the instore pickers - the online order system sometimes throws up some strange alterntives for items not currently available. One other minor point is that I always request my order to be delivered with bags - however on occasion, at least one tray will turn up with unbagged goods, which can be annoying. Finally, there are occasions when products arrive with a much shorter than expected life - they normally announce these on the order sheet (but not always). However, compared to other home dleivery services, Tesco a definitely better than most.