Novoflex products have a good reputation for quality and durability. I use a Novoflex adapter on a NEX-7 and it's excellent; solidly built with well finished materials, snug fit on the camera - no looseness at all. My Leica lenses have a positive mount with no play, and the release lever has good travel so there's zero probability of an accidental release. I'm sure the adapter for the X-Pro1 will be of equivalent quality.
If you live outside the US you can buy directly from the Novoflex web site at a reasonable price. Here in the US Novoflex products are distributed by HP Marketing who add their usual high markup so the adapters are quite expensive. Novoflex cannot not sell directly to US customers.