While it may only serve to confuse more than help - it's been shown that the quality control of any/all of the Chinese in-frame kits is highly variable, regardless of vendor or "brand name" and even the advantage of a warranty becomes questionable when you consider the relative cost of a replacement part vs shipping and handling, wait times & even if a merchant will honor the warranty in the first place...
It seems to me that the quality of the kits has been slipping, "name brand" or otherwise (not that they were ever particularly great lol) and yet the prices asked by the larger retailers have been continuously rising. All of these kits are a roll of the dice and with that in mind - I would personally find the least expensive kit from any retailer regardless of promises, one that has at least some good reviews though (so you know you'll get your purchase) and if the engine proves defective, simply getting another engine - keeping the first for the replacement parts you'll eventually need as S&H alone both ways for a defective engine may well in itself be close to 1/2 the cost of just getting another "engine only" to replace it. This is especially true with individual components such as a scratched or dented tank, malfunctioning mag/CDI or whatever.
Please don't get me wrong, I do love these lil engines - but make no mistake, no matter who you get it from or how much you spend on it it will be poorly assembled and may have damaged or missing parts. It's best to consider the engine itself as a "kit" only loosely assembled and requiring you to give it a light once over, cleaning it up and assembling it properly - which really is easy given the simplicity of the design... with that in mind I should prolly mention most/all of the black engines suffer from a horrid paint job as they all seem to be hurriedly repainted silver ones, you might wish to get a silver one and paint it yourself *shrug*
Expecting quality, good customer service & honored warranties and a willingness to pay the extra required for such is most likely best reserved for the custom aftermarket parts you'll no doubt end up wanting