It's not something you buy in lieu of a Webley. It's something you buy, because you already have a stack of Webleys and a Webley-Fosbery in your collection. And it's also not a "reproduction" Webley, it is a seriously updated, bespoke gun.
Put another way, you can ask, "Why would I spend $125,000 on a custom Porsche 911. When an off-the-lot Volkswagen Beetle will get me from Point A to Point B just fine? Afterall, Porsches are just fancy VWs..." That is simply not the point.