the plastic round ones are suppose to cover the hole up and insulate it but if one of those plastic tip ups freeze in your hole most likely it will just shatter in pieces if you try to pry it out
the wood ones will freeze up on you more but they are longer and is easier to pry out .
I personally made my own tip up the wood is shape like Beaver damns but the hole is completely cover by wood
next time im out ill take a pic of it
I also have a buddy when it gets real cold he takes one of those battery operated aerator for your bait bucket and throws it in the hole
