No comfort
I have bought many hot water bottles over the years and use them almost daily.  These are disappointing.  They are a stiff thick plastic, smooth on one side with spikes on the other, that does not conform to your body.  In my opinion, they do not radiate heat well and bring no relief or comfort.  Since it is too late to return them, they're already in the bag destined for the local thrift store.
Rating: 2 stars