From a safety point of view
First off, I'm not a welder. I'm the EH&S manager for an industrial service company. We have tig operations in 2 fixed facilities as well as multiple on-site piping jobs (some with as many as 30 welder/fitter teams going at once) all over southeastern Ontario.
At first, some of our seasoned guys scoffed at the idea of a handheld tungsten sharpener saying things like "If we buys those things the young guys will never learn how to do it any other way" and "as long as you know what you're doing, sharpening tungstens with a bench or handheld grinder is perfectly safe" and then my favorite "sharpening tunsgsten with a grinder is the way its always been done". Well, from a safety point of view, holding a small piece of metal (often sharp on both ends) and sticking it into a rotating grinder without the benefit of a steady rest is just an accident waiting to happen. And guess what? It did. We had a 16yr veteran drive a tungsten into the meaty part of his palm in an instant of carelessness. After that the decision was made. 6 months later, everyone loves the handheld units. Now the site supervisor can have a laborer sharpen 100+ tungstens at the end of the day and we are not paying a welder/fitter to do it. They are always consistent and contamination is a thing of the past. We bought 10 units and it was the best $3000.00 we have ever spent.