I know how to use a spindle like that although I must admit I´m not very good at it. My experiece is - it is a lot slower than spinning with a drop spindle and I tend to get cramps in my fingers after some lenght of time(but again - that might be because I´m not good at it). The advantage: You are much more mobile. If you fancy taking a walk while spinning the spindle won´t dangle between your legs and get in the way. You also don´t even have to look at the spindle while turning it - something I found very convenient when I was spinning while simultaneously listening (and watching) a presentation. Plus: As the yarn just jumps over the tip of your spindle while spinning you don´t have to "unhook" the yarn every time you want to wind spun yarn onto the spindle.
LG
Bea