It is beneficial for real changes to be propagated quickly, but it's irresponsible to use real traffic, so they used a test prefix -- a range of addresses without users.

Trusting / untrusting isn't likely to be the difference between propagating the route in 10 seconds vs 60 seconds. That's not enough time to do anything meaningful trust wise --- either the provider checks the routing dbs and routing PKI or they don't, but a survey of providers that accept or not poor routes is another story.