I've been told someone else can offer me the same sash window, can that be true?

A: Emphatically NO.

Don't be fooled by other companies' claims. If someone (other than a registered Bygone Installer) claims they can offer you the same double glazed sash window, THEY are lying; ONLY Bygone preferred installers are able to offer the Bygone Collection sash windows and only installations via an approved preferred installer are guaranteed by Masterframe Windows Ltd.