We've had three supplemental brake systems since we started towing. The first was was a Brakemaster from Roadmaster that worked great with the air brakes in our coach, but was a minor inconvenience every time we used it. There was an air cylinder that had to be attached to the brake pedal every time, and this was only really an issue every time it rained it seemed as I'd be on my knees hooking up the cylinder in a puddle.
When we downsized to a small class C, I installed a Roadmaster Invisibrake. Once installed this system required nothing to hook and unhook when towing other than the tow bar and electric and safety cables. It worked perfectly, but went away when my daughter got the Jeep.
When we replaced our old Jeep with a new one, I installed a US Gear Unified Tow Brake and love it. The reason I didn't buy another Invisibrake was cost. I found a brand new UTB on ebay for $499 so went that route. I'm a self install type person, and for me, the UTB was the easiest of the three systems to install.
Of the three systems I have personal experience with, I'd recommend 'em all, except that the Brakemaster had to have the air cylinder installed/removed every tow, and it used brute force to operate the brakes instead of using the towed vehicles vacuum brake booster. From an operational standpoint, I prefer the US Gear UTB to the Roadmaster Invisibrake as it is adjustable from the coach for different driving conditions. Both the Invisibrake and Unified Tow Brake have vacuum pumps to energize the towed vehicles power brakes for more efficient braking.
Another system you may hear about is the ReadyBrake. It is a surge brake system that uses a cable hooked from attachment point on the RV all the way to the brake pedal in the towed vehicle. The design is quite simple with no electrical parts, pumps, relays, etc to fail. This system uses brute force to operate the brakes like all non-invasive systems. Few drawbacks I've read such as issues unhitching when pointed downhill, and cable breakage. It seems once properly installed, most folks really like 'em. I prefer a proportional system with energized brakes.
With the setup you describe, I think you are making a wise choice with the Air Force One and will be happy with its performance. Be certain that a battery charge line from the coach to the toad is installed, or you may find your Sonic with a dead battery after extended towing. I learned that our Jeep without a charge line would drain the battery after two or three days of continuous towing... depending on how often I had to use the brakes as it's the brake lights in the towed vehicle that run the battery down.