I saw someone using this on Youtube making musky flies and I knew I wanted it. I have been making tube fly's for about a year now and keep having issues with the tubes slipping around the mandrels. I still use the mandrel but can fit the end of the tube into the mouth of the vice and what a difference that makes. I like the HMH vice configuration in that its a nice straight profile that works great for wrapping or checking on all the sides of the tube fly as you work.
It fit on the HMH Spartan vice, but the HMH website claims to have one specific for this vice and the standard vice they sell. So I am wonder if they started making different sizes now.
If you are serious into making tube fly's I highly recommend this.