I would call them and make sure that "adapter" will work with a SxS. They're rather vague, at least what I looked at.
Between images of shotgun & custom applications it sounds as possible fit. whether the basic setup will work on a double gun (SxS, O/U) would seem to depend on if the standard mounting strap is long enough to wrap around both barrels along with the shim. If so, then you would be able to get a valid reading on both barrels without re-positioning the mount.
If not, the custom version could take care of that or have a bench/table/etc mount made.
Looks as if the regular price is $399. There was a pre-release version for half that but they have sold out of that run.
