I’m a republican but given that we have a monarchy I would say I think it’s beneficial to the charity for Prince William to draw attention to it. However, I think that whilst the royals can have as many homes as they like, they should absolutely not be using public money to do them up, maintain, and furnish them. That should apply in my opinion whether the home is privately owned or owned by the state and loaned to the royals. I understand why William and Catherine would wish to have a residence out of London when they are bringing up young children and Windsor is a nice little town ideal to raise a family. I assume they need to retain their apartment in Kensington Palace as all the working royals need a London base. Their Norfolk home is presumably their country home.
As for myself, I count myself as lucky to have one home, and to own it.