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I've had them before and they look cool, but I'm not sure that they actually "protect" anything since the hose itself is more resilient than the protectors are. They can be useful in identifying the type of gas though (yellow for octo, green for nitrox or O2, etc.) Trident makes some.
The best way to put them on is to pull back the rubber hose ends and to put them on inside out on one end with electrical tape, then fold it over (right side out) and glide it across the hose. Put the other end down with the same tape and then you'll have the ends covered with the rubber hose ends so the install looks clean.
I recently removed the last one of mine, since they started to fray.