I guess I'm not following how this is anything other than a play on wording. With flat rate and contracting the client gets the final price before the work starts. The exception would be something like finding a splice in a wall you open up. The form I use with on-site "flat rate" bidding is nearly identical to my contract in language. The main difference is that it has lines to write in since I don't have a laptop and printer on the truck.

I never bid work that I don't see. With cans, is there a spacious attic, tight attic, or remodel from below? Is it in the living room with a high sloped ceiling. You have to adjust with any method of estimating, but you end up with a set price.

With T&M you have a set rate, but the end result is variable which creates stress during the installation and for the client when they get the surprise at the end. Clients are much more likely to negotiate with T&M invoicing than flat rate or contract.

Dave