Aside from the obvious slight differences of burst and output and efficiency, a lot of the differences are in the subtle details. The NT tends to flicker under certain circumstances at low levels, the Ra won't. The Ra is calibrated precisely at every level, the NT isn't. The Ra should have ruler flat regulation, the NT... comes close enough. The Ra is a bit longer due to internal springs that protect the battery from hard impacts, this makes it tougher and more comfortable to grip for some. The NT is shorter, making it more pocketable for some. The Ra uses a glass lens protected by a thick steel bezel and rubber rings, the NT solves the problem by using a plastic lens, which works fine but is more prone to scratching. The Ra will probably have a better tint, even if you don't spring for the GT option. The Narrow beam Ra will out-throw the NT at the same output, the Wide beam will probably throw about the same. That's about all that comes to me off the top of my head. Then you have the issue of the company behind the lights. The Ra is made and backed (seriously, if something goes wrong, he's got your back) by Henry, a long time friend of ours and a good guy. NT is a little on the shady side, and that's the reason I won't be buying anything else from them, even though I like my 120P and use it more than just about anything.
I think it really comes down to personal preference and at what point you're satisfied. If you can find an NT for under $100 and it satisfies you completely, go for it, you just saved a lot of money. If quirky little problems bother you, you might want to consider stepping up to a Ra. The subtle improvements of the Clicky are worth the somewhat staggering price to me, but I realize there are a lot of flashaholics on a budget who want an advanced light and wouldn't really benefit from and be able to justify the cost of the extra refinement. Though I don't personally like them, it's kind of nice to have another company offering a similar light made to a cheaper standard.
Anyone have anything else to add?