Very poor functionally. Panasonic says that you cannot change the type of battery that is used. Their suggestion is to buy new phones that have different batteries. Crazy!
Costco just started carrying these phones. There will be millions of expensive headaches!
PS When our phones went dead Panasonic's batteries were on back order.

My suggestion is NOT so buy products from a company where the usage of the product causes a problem they do not cover. If you are willing to replace the battery yourself every 3 - 6 months of use, it is probably a good handset.

Personally, I will not buy another Panasonic product.

Two features stand out in comparison with our retired Siemens phones, one negative and one positive. On the positive side, these phones support detection of voice messages on an existing message system, so that it is easy to see from any handset whether there are unplayed messages on either line. On the negative side, the system does not support handset naming. We imagined this would be a minor inconvenience when we bought the phones, but it has proved to be a major drawback: there's simply no way to get the entire family to learn what number goes with what phone. When we had the Siemens system, which supports handset naming, the we had a working intercom system (not to mention convenient transfers of calls); now we're back to shouting.