I'm skeptical of the value of these services overall but the more I think about time savings and not having to worry about keeping up my otherwise-useless food-buying skills they could be worth it, though only if they all but completely removed my need to grocery shop. And I think the prices would still have to come down a little more.
What'd be more valuable is a grocery store with online ordering and curbside pickup with some kind of enforceable (like, with real teeth, not "oh yeah, we tried to screw you, here's a voucher for the $1.50 difference, bet you're glad you spent two hours getting us to pay up!") guarantee that they wouldn't sell me anything over the average price for my area. Infeasible now, but imagine if government tweaked the information imbalance to be a bit less out of customers' favor by mandating (or incentivizing) machine-readable posting of prices week to week... then such a service could exist, could be audited, could be more-or-less trusted. And would save huge numbers of hours and lots of fuel for driving around comparison shopping and other useless consumer BS we (those not rich enough to pay others to worry about this useless crap) currently put up with as practically a second job.