I think it is usable as a first name or middle name. It’s personally not a name I would use but I wouldn’t feel negatively toward it. [name_m]Fitzwilliam[/name_m] provides plenty of nickname choices.
I love it as a first or middle. I stumbled across an IG that had a newborn [name_m]Fitzwilliam[/name_m] they called [name_m]Fitz[/name_m] and it really sparked an interest in me.