I am amazed there is a guy building these, and the price seems very reasonable.
He's creating a custom collet clamp, and IMO that is the only alternate way to do it, but to be done properly, it requires some good machine work with tight tolerances, and the issue I see is that bores are not always concentric with the outer diameter. On my own Ruger MK2, I turned the muzzle threads and found that the bore was out of concentricity by a full 0.015". So all I can think is "Watch out for baffle strikes" with any sort of clamp-on device.
Surprised to see D.A.Q.'s listing, he has been around for a long time; if memory serves correctly I first ran across him in the SN (Shot Gun News )
when the internet was two Dixie cups coupled between a tightly pulled string.
I still have his list from long ago if it is still the crusty but quality machinist.