The only one I've ever used is my Darex M5. I purchased the unit when I lived in Phoenix because a shop I worked for was drilling a lot of weldments and I got tired of using beat to "s" drills. After the shop owner saw me using it he agreed to pay me to sharpen the shops drills on the side. It didn't take long for me to pay for the Darex M5. I haven't had the need to use it since.
In any case, the point of this post is that it seems to me that many people expect that you put a beat to "s" drill in a drill sharpener and it automatically gives you a perfect drill with split points and the web properly thinned. The Darex M5 certainly doesn't work like this. You have to adjust it and keep tweaking it in till it's right.... then you can do other drills which are the same size without adjustment.
With the large drill attachment and I think one for small drills I believe I paid like $1,300 for the Darex M5. My M5 has diamond wheels and easily does cobalt drills.
Once you have things dialed in on the Darex M5 you get a drill that easily holds size and that drills properly.
Since I haven't used other drill sharpeners I wonder if with other drill sharpeners you can sharpen a drill without the need to tweak the drill in if you change drill sizes? If something like this exists if it's as portable as the Darex M5 and what is the cost? For what it is and for what it costs I have found the Darex M5 to be a decent piece of equipment.
Jon Banquer San Diego, CA