I use Instacart because the experience is better. Their prices are roughly a 5% markup over Safeway (and now, I assume, Trader Joe's), which amounts to a few dollars on my typical grocery order.
That's more than made up for in the convenience factor. There's a huge difference between being available to take a delivery during a 1-hour window today vs a 4-hour window tomorrow. For 1 hour, I can do highly interruptible activities (checking email, tidying the apartment, reading a book, etc.) without a significant negative impact on my overall productivity. It's a lot harder to find a 4 hour block of activities that offer the same kind of flexibility.
That's more than made up for in the convenience factor. There's a huge difference between being available to take a delivery during a 1-hour window today vs a 4-hour window tomorrow. For 1 hour, I can do highly interruptible activities (checking email, tidying the apartment, reading a book, etc.) without a significant negative impact on my overall productivity. It's a lot harder to find a 4 hour block of activities that offer the same kind of flexibility.