Adapting to what your opponent is using and doing will be the best guide. Offensively they are nice, while lesser in range and defense compared to rebel troopers, with your current build 5 points less than them too.
Choices choices, that never ending dilemma to advance or hold back. They seem to be built for close range offense rather than defense, certainly use best cover since they aren't as defensively strong as rebel troopers with nimble. If your opponent has range like DLT-19 Stormtroopers, you'd be wasting your points and unit keeping them far back in cover as they reasonably get chipped away to nothing. While, I wouldn't suggest to rush in going head to head vs. Snowtrooper unit with a Flametrooper.
I'd agree with Shanturin, should use more rebel troopers than fleet; and maybe use Rapid Reinforcements with them when able. The way you have it now, I'd say move your fleet trooper up going cover to cover while the rebel troopers provide cover fire attempting to protect them. or if playing Breakthrough, perhaps just keep them in the back separated as deployment zone defenders.
Ultimately, I go back to and expand my opening reply. Adapt how to use them based off what you are using, what your opponent is using, how you'll be using your units, how your opponent will be using there unit turn by turn, and deploy set up. That will serve you the best in greatest majority of situations, hope that helps and inspires new ideas.