But can they seize your phone and crack it and look through your stuff without your permission or getting a warrant/judicial oversight? Otherwise, the only thing this does is add one extra step ( and additional cost which doesn't matter since taxpayers are footing the bill ) for the Feds to break into your phone.
Law enforcement is permitted to do that only if they have a warrant. The question is whether they can compel you to give up a password (mostly no) or compel you to give up biometric key (unknown, but this court says no). And it is not just an extra step. Cracking an encryption is infeasible or extremely expensive when properly encrypted.
This depends highly on your threat model. What your local sheriff's office can do, versus the FBI, versus the NSA. Mall security Rent-A-Cops can peek through an unlocked phone, but probably aren't going to be doing any kind of cracking other than the obvious possibilities.