I can think of a couple ways to improve the "flexible reinforcement budget" booster.

[Kev]

Currently, it decreases how long you have to wait when your reinforcement count is depleted (from 2 minutes down to 1:47). The only time you might get some use out of it is if you're doing a solo mission that's way too hard for you, and you spend lots of time running because you're waiting for your reinforcement count to come back to give you another "suicide run" at the objective.

Here's two better ways this booster could work instead:
1. When your 2 minute reinforcement timer is finished, you gain reinforcements equal to the number of players instead of just 1.

Or...

2. As soon as your reinforcement count falls below the starting number, a 5 minute timer to replenish it starts immediately. So if you have a full game with 20 reinforcements, and someone uses 1, the reinforcement timer starts right away, so you'll get a free one 5 minutes later, and another one every 5 minutes until you're back at the max. When you run out completely, the timer will go to 2 minutes as usual unless your previous timer was already below that.

EDIT: or how about option number 3: every primary or secondary objective you complete grants you an extra reinforcement, kinda like the first game did when you were playing solo.