Plumber, I would never rely on that hechsher, but it’s not any less kosher than something without a hechsher, about which you can’t technically say “it’s not kosher”, unless you are referring specifically to a non kosher item.
Take, for example, a deli with Tablet K bagels. While I consider it highly irresponsible to allow a kashrus certificate to be hung in an establishment serving Boar’s Head, and I would certainly not eat the bagels, I dont think you can say with certainty that they’re treif.