I am in the process of test fitting one. I'm a BKA and have been wearing a Alpha pin locking liner for about a decade.
No matter how well my leg fits I tend to get a lot of pistoning with the regular Alpha liner. This is both uncomfortable and leads me to run through liners very quickly. It's not unusual for the end of my Alpha liner to start separating after 6-8 weeks of normal wear. I've shied away from traditional vacuum systems because of the extra layer required to seal the top of the socket. The V-Pin seems like an interesting compromise so I decided to give it a shot.
So far the feels good but I've only been on a test socket for a few hours at a time. In the short time wearing it around the house I've noticed that bending my knee seems a bit more difficult due to the extra liner thickness. They say that will get better as the liner breaks in but time will tell. I expect to have the final leg done in a few weeks. When I've had a chance to really put it through its paces I will report back here.
If anyone else has experience with this I'd love to hear about it.