In the company's text it states that they are for 383-440.
It wouldn't make sense for them to require a larger bore size than a 383, because then they would only work on 400's and 440's. No 361, 383, 426 wedge. It would restrict their market.
I also wonder how well they are made and what kind of testing that they have done. Not just for performance, but what kind of durability testing have they done to prove out the strength of the design? How severe are the test parameters etc? What quality measures are in place to make sure that all of the parts are good?
Just because it looks good and fits, doesn't mean it will last under severe environments.