1. The time slot changes as soon as you click checkout, what I mean is while browsing I'll always see "Available Within 1 hour" then when it actually is time to checkout that option is gone. It happens virtually every time and I've never seen it happen the other way around or happen while shopping and refreshing or going back and forth between shopping and checking out. This leads me to believe it's an intended trick they are using to get people to shop even if the time they want isn't available.
2. They don't provide drivers with any sort of cart to actually deliver the groceries with. One delivery driver had to lug water bottles and other heavy items from down the street where he could find parking into my building and up to my apartment. Amazon Fresh gives their drivers a handcart to help with deliveries.
3. After several orders of mine were never delivered and Instacart offering a $5 credit (after wasting hours of my time waiting for their large delivery window) I had a driver tell me that drivers get to keep orders that are not delivered and sometimes they pick really good orders and say they couldn't be delivered.
I still use them because it's convenient but wish they would treat their users with more integrity and also manage their delivery drivers better by providing supporting tools like a cart or keeping tabs on drivers that may be taking orders for themselves.