I've tested the door lock and doors I've used it on, it does actually work if you set it correctly and it fits the door itself.

For both, it depends entirely on the door itself, and neither would stop someone determined kicking through the door. I've stayed in plenty of places where the deadbolt wouldn't work with the strap, but those are also places where the doors were made in China or Turkey, so nothing is standardized to EU/US/Canada specs.

A regular ol' rubber door stopper often does the trick just as well. Layer your security.