Didn't ride the Garage but I'm pretty sure it's Rome's pricepoint park board (we did ride the Factory Rocker, which is their all-mountain budget board). The Factory was really a solid board given it's price. You're not gonna be wow'd by a laundry list of innovative tech, with the budget boards they keep 'em pretty simple to keep the price down, but if the Garage is like the Factory, it's gonna be at *least* serviceable for ya.
Yes, it's rocker, so yes it will be quite a bit looser than your cambered Arbor. At higher speeds it's definitely going to flap around it's just not going to be as damp, and it's not going to have the same edge bite as a cambered stick, either.
Don't try to ride it like you'd ride that Arbor or you're gonna have a bad time
take the opportunity to work on different type of riding, I think the Garage would work well for getting in to butters & flat spins on the ground since it's gonna be pretty soft and loose.