The image you get from second party kits may look good but you have to look at color fidelity, grain and sharpness for starters, and then in the long run current E6 films use a proprietary dye stabilizer that must be accounted for.

So, you may not see defects unless you look carefully at comparison images or compare them as a function of keeping.

In addition, the push/pull characteristics of second party kits may not be the same as the Kodak and Fuji products.

Please be aware of this.