The pull-out hose puts less stress on the valve. And you weren't stressed to start with. It's all very well hauling a giant pump around, but all that leverage can snap a delicate valve stem right off. Our presta-only head sits on a short pull out hose to give more options on where you pump from and fewer chances of your rippling muscles pulling the thing clean off. We weren't using that space in the barrel anyway, so the hose doesn't even affect the pump's efficiency.
Thread on pump head automatically adapts to Presta valves
Rebuildable internals parts avaialble aftermarket.