The seals for both valve types are, as already described, not always 100% leak-proof, but I've found that there's more to proper attachment of going ... on a bad day 2-3 times solved and fixed again, then it works. And that has not a bit worse in 6 years!
I also always find class that is "short" setting for pumps for the last Hochdruckhübe, get as a bicycle / moped tires with little effort to loose 4-6 bar.
I would buy again! although SKS many "cheap pumps" builds, this here is worth every euro.