I've got a lot of Grafs out there and two leakers. But both were also very long in the tooth. I've seen the Saleri and what it is NOT is PLASTIC... it's an epoxy resin. The claim is that they are used on some of the exotic Italian vehicles, which have very high rpms and are quick revving. Both would be indicative of fatigue for the pump impeller and the bearing, but I don't have any history for life expectancy for anything except what I've personally used. None of the companies give failure or life expectancy reports.
I do know that all the castings between the plastic, resin, and the brass impellers are very fine. However, I don't have any worries that there is a tremendous advantage having a very smooth impeller. I don't thinkVW has undersized the w.p., as there aren't many issues even in very hot climates with any choice of w.p.
As someone said, I abhor the Meyle stuff, most particularly any o their products with a sealed bearing.
I only know that all w.p.'s have a failure rate. They are supposed to not fail for 100k. I have not had a Hepu seal fail, but others have. I might also note, despite the number of failures of the OEM plastic impeller, they go in every single vehicle and we really only see comparatively few fail. Those get loudly advertised. I've taken out a lot of perfectly good ones and also my share of leakers that were OEM... Only a few OEM broken impellers.
Beside avoiding the obvious bad choice, Meyle, keeping your eye on the water level and checking for possible leaks is the thing to do. Use what you are comfortable with. I can't guarantee that any company always makes a perfect one.