Without the roll bar, I cracked a head, motor mount, fuel tank and both shock towers. With the roll bar, I have broken a rear shock tower and a bunch of gas tanks. Came to find out that my gas tank breakage is due to the fact when landing on the rear shock tower, the RPM plastic bends so much that it smashes into the back of the fuel tank.
I think your in need of both things.
The RD Logics cvd's have held up to about a half gallon in my 21 (2.5 hp) maxx without any wear at all.
The roll bar is scraped up, but seems to protect a lot of stuff. Roll cages suck to work around, but they do tend to protect a little better.
Sorry, rambling. Just wanted to let you know that both are a good investment. Regardless which order you get them in.