I just put this out on my toddler's activity shelf this week. To introduce it, I took off one lid and took out the block. I set them on the mat and did the same for the next container. After all three were opened I showed how to put in a block and find the lid.
This jar has a twist lid and I wasn't sure how difficult it would be. She puts the lid on and pushes on it and it seems to stay on without the twisting. When I see her using the activity I try to casually model the twisting.
The square lid is a challenge putting on. Sometimes she gets it, sometimes not. A younger child would do better with all circular lids as they are the easiest. (A younger child may also need to start with just one container w/ lid) She has no problem pulling all of the lids off.
Another aspect of this activity is the one-to-one matching. (One block for each one container.) One-to-one is a very important pre-math concept that is needed for when a child starts counting. I am always trying to find ways to incorporate this skill into my toddler activities.