I see their work product with some regularity. To say I'm not impressed would be a severe understatement and I really don't understand why companies keep hiring them.
It was mostly regurgitating the AWS published best practices on Deloitte letterhead. We all grumbled how "this was not a good use of money", but one of the senior folks from the line of business side said "you guys were going to basically do this anyway...now noone can say you picked the wrong strategy". Which, to be fair, was true.
So that's probably why companies keep hiring them.
meaning: If your boss won't bother to ask it's own employees or trust their feedback, he might choose a well kept, well presented third party to gather that feedback from their employees, and then package it nicely with some cool logos and slides and decks, and charge you a shit ton of money out of it.