I'm in the process of doing one of my tail light setups on a customer bike and while removing the old I noticed the weld connecting the mounting bracket to the license plate back was cracked from top to bottom. This un-named unit has a two piece steel construction which is just a piece of 1/8" welded to a piece of 3/16". Herein lies the problem. Thin steel bolted way out back on a rigid framed bike (Sportster) in this case acts like a tuning fork. Hang 2.3lbs off that combined with half seam welds and shake it at lets say 5 beats per second and it's bound to break. The assemblies I'm producing have a full 1/4" 6061 aluminum construction and weigh just under 1.5lbs. They also have an 1 1/4" offset mount which moves the plate closer inboard reducing stress on the bracket as well as keeping your bike looking clean and not goofy.
You could spend $120 on a generic model A assembly, bolt it on, take a step back and say: "Nice! now my bike looks like every other guys!" Ride it, have it break and then spend another $120 or you could just buy quality to begin with.