Works pretty well!
The chalk holders are sturdy, and hold even really small nubs of chalk tightly in place. Although it's obviously easier (and faster) to simply grab whatever piece of chalk is resting at the board, I find that whatever I write using the chalk holder usually ends up being more legible -- which is, of course, the point.

The four-star rating is due to the twist-grip of the chalk holder itself. I prefer the clutch holders since it's easier to fully retract the chalk (and not get it all over you, your clothes, your bookbag, etc.), but with this one, I find that I never fully retract the chalk since it's inconvenient to do so.

This product is all metal and very durable. The end must be unscrewed and screwed back down every time you need to extend the chalk. This can be somewhat annoying when you are trying to lecture as it slows up your pace when writing notes on the board. Now I use them for my colored chalk, which I use less frequently, and went back to my spring-activated chalk holder for white chalk.

I bought this product for my husband. He told me he loves it and would recommend it to other teachers.

If the chalk breaks, which happens easily against the metal edges, especially in the hands of enthusiastic junior high students doing board races, you have to unscrew the top and use the edge of a paperclip, or other sharp, thin object, to push the chalk up so that it can be used again. This tool is much sturdier than the plastic variety, but doesn't have the button on bottom that you can push for easy chalk release and refill.

These chalk holders were a great investment. They are expensive, but worth every cent. They really grip the chalk very firmly - other chalk holders that I have used in the past do not grip the chalk very firmly at all, with the result that the chalk was inevitably pressed back into the chalk holder the moment I started writing on the blackboard. I keep two or three chalk holders at hand for every colour - in case the stick of chalk breaks or gets used up during the course of a lesson. (Breaking of the chalk during writing can be avoided by letting it protrude no more than a centimetre from the tip of the chalk holder - but then it may not last the whole lesson.)

I keep a set of the Commando chalk holders in a plastic pencil box in my briefcase. I use the clear anodised chalk holder for white chalk; the gold anodised chalk holder for yellow, orange and red chalk; and the blue anodised chalk holder for green, blue and purple chalk. The chalk holders look very professional, and best of all - they stop my hands getting covered in chalk dust!