We just used Garden Grocer for the first time a few weeks ago. It was a short trip, just 4 days so we didn't want to waste precious time having to go out shopping. Also we flew down after school and had a 9:00 pm landing with 10:00 pm arrival at OKW.
In this situation it was well worth the extra cost & convenience.
We flew on SWA so I had plenty of room to pack a lot of non-perishables so I wouldn't have to pay such high prices for everything. (Cereal, oatmeal, coffee, filters, etc)
It was really nice to have fresh milk for my coffee, OJ, choc milk for ds14, grapes, bananas etc.
I would use them again when only using DME for transfers. It's still cheaper than calling a cab.