Bottled bacteria might be an insurance policy. On one hand, mulm from another (trouble-free) aquarium probably has bacterial fauna that suits the local water chemistry; on the other hand, if the client is paying $15,000 for a set up, I might consider using bottled (presumably) sterile bacteria. It all comes down to economics, risk, reward, and belief in one or other product! I would like to give these boittled bacteria a try and see what happens.
I think I recall some famous aqua-personality, whose leg has been pulled in recent days far too much (probably), who would say about substrate "dirt is dirt whatever you call it and however you price it." That line of thinking would surely also say, "bugs is bugs whether they be in a bottle or sloshing around in the mulm."
So much to learn....