Call the Vader guru, Pete, of Kronik Racing if you are interested in the Boomcat. The company Baodiao, distributed by Boom in the US, manufacturers the Vaders and the Boomcat, and all are actually 50-state EPA/DOT certified in the US (rare in the US as most Chinese bikes are 49-state certified; Californians need not apply). I believe the Amstar is also 50 state legal as I recall seeing one at Kronik Racing when I lived in California until a few months ago.
The Boomcat is a good bike for speed in the 125cc class, since it sports 17/17" wheels vs. the little wheels all the Grom clones come with. The Boomcat is actually certified on the same EPA/DOT and CARB certificates as the Vader series of bikes, so if people have registered Vaders, you shouldn't have an issue with the Boomcat. I do know that NJ uses the EPA/DOT list to register bikes, although someone recently posted that they use a list from a few years back, but again, lurk around the Vader forums or post here in the 'Street' section and see if anyone has registered a Boom Vader in NJ. Generally, when someone jumps through all the red tape in their state and becomes the first one to register a particular brand/bike, it is much easier for others to follow. Hopefully, that is the case with a Boomcat.
www.kronikracing.com