No need to be coy: by itself, the Rumbler isn't a big draw. It's an utterly strange design, and looks like something you'd see in one of those traveling carnivals that set up in deserted department store parking lots. The Arrow ATV may have been fine on its own, but for the Rumbler you've really gotta splurge on the upgrade kit.
Upgrading with weapons, the Rumbler transforms from a light weight excavation vehicle into a heavy duty ground assault vehicle. Weapons provide unmatched attack firepower and makes [sic] the Rumbler an extremely formidable assault vehicle.
While the ATV add-ons had a bunch of guns and armor, the Rumbler's is much less involved: in fact, it only adds three pieces to the vehicle, and two of those are a matched pair.
To plug into the front of the Exoskeleton, we get the Armored Thrasher Claws. The main review already pointed out this body looks similar to the Synthoids, and so these would be its arms. They're just a pair of appendages with organic hooks at the tips, sort of like a praying mantis' arms. There are silver armored plates at the "wrist," pointy pieces that would aid in slashing. Although the product images suggest the arms are meant to fit in horizontal to the ground, like they're going to grasp something in front of them, the sculpt makes it clear they're meant to be perpendicular, for clawing at the dirt.
On the back of the car we get the Armored Scorpion Whip, a large tail that curves up over the cockpit. It doesn't end in a stinger, but rather two small orbs, suggesting it can fire some sort of energy blast. It's got a very "War of the Worlds" feel. The post that allows it to attach to the rear exo arm is too long for the hole, so it sits up higher than it should. I dared to customize mine by carefully slicing off a quarter centimeter or so - after all, if I messed up, getting a replacement would just be a matter of $1.25. It's bent slightly to the side, so it doesn't hang in front of the driver's face.
Alone, the Rumbler doesn't look great. I saw it in the store several times while I was on the hunt for Amari and Riptide, but never bought in. I finally decided to give it a shot, but only with the Weapons & Armor Pack added on. Together they make a pretty threatening contraption. The Armored Thrasher Claws add enough weight to the front of the vehicle that, unless you have someone heavy sitting in the driver's seat, the whole thing will tip forward, lifting the rear wheel off the ground. Whoops!