Very bad as they don't work even when sitting next to each other. I expect it is something to do with conflicting wi-fi signals from home broadband/cordless phones/remote controlled toys. However I suggest that this product is not fit for purpose if it cannot work in this type of home environment. As they are delivered in blister packaging they are difficult(impossible) to return once opened.
The price arguably reflects this quality issue, however if they don't work then they are worth nothing. Avoid unless you live in a non-urbanised area with no home wi-fi or cordless phones.