I don't believe I've used Tetenal's 3-bath kit, but I have used at least two others (Paterson Chrome 6 and another brand whose name I don't recall, but I believe they make Freestyle's Arista-brand E-6 kit. I found that neither produced results that were as consistently good as what I get from Kodak's kit. Both of these 3-bath kits are advertised as being intended for reuse -- that is, you mix up 250ml (or whatever), process a roll, store the chemicals, and then process a second and third roll. I found that results on the first roll were usually fairly good, but the second and third rolls seldom matched the first roll. This problem was particularly bad if the chemicals were stored for long between uses, but even doing two rolls back-to-back, the second roll was usually too dark and the color was a little off. For a low-volume user such as myself, this was a big drawback; it raises the cost to the point that Kodak's (nominally single-use) kit is less expensive, and/or the need to save up and run two rolls back to back vs. processing two rolls at once in more chemicals eliminates the advantages of a simpler 3-bath process vs. a 6-bath process.
As to claims of poor archival qualities when using 3-bath kits, I can't comment from personal experience. My own perspective on this is that since I can't test it myself, I'd rather play it safe and use a product that's most likely to produce long-lasting results. This means Kodak or Fuji E-6 chemicals. Since I don't know of any place that sells Fuji chemicals in anything but industrial quantities in the US, that means Kodak for me. If I were forced to use a 3-bath kit, I'd consider using C-41 stabilizer on it. I figure that would be unlikely to hurt, and might help, archival stability.
