As you may know, I have dabbled quite deep into bleaches and BLIXes, so I claim to have some knowledge about what they do, and I have processed hundreds of rolls myself. My old slides (souped in Tetenal's kits) look just as good as the ones I did later with separate bleach&fix. There are some amateur kits which took some rather questionable short cuts, but there are BLIX kits out there which consistently deliver excellent results.
Rudi, I don't doubt that you got good results. But here's a few things to consider:
Does the aftermarket blix have enough capacity to handle some heavily (or over) exposed rolls? How about a couple such rolls in a hand tank? What about other films - are some more difficult to bleach than others? (Maybe some of the easier films have some sort of bleaching "accelerator" built in?)
How about the situation where the blix is in storage for some time - does it lose bleaching power?
I don't know the answer to these things; maybe it DOES continue to work fine; but I tend to be skeptical unless Kodak (or Fuji-Hunt?) has put their stamp of approval on it.
At any rate, my experience is mainly with the Kodak formulations used with the low speed Kodak pro portrait films. With those, in a cine processor running at 50 ft/min, and maybe 3 to 4 hundred gallons of bleach in the processor tank, we had to keep constant aeration in the tank - a continue layer of bubbles on the surface - else the bleaching would fall off. (This is per the Kodak control strips, which have a "bleaching test" that helps to stress the bleach, for an early warning.)
At any rate, incomplete bleaching is not that big of a deal. Retained silver doesn't affect longevity of the image as far as I know, and the film can always be rebleached if necessary.
Ps, on this about this a bit further, I've sometimes been puzzled by something of the internet lore about overexposed color neg film giving a pastel-sort of appearance. Now I know from experience - very seriously-controlled testing, albeit over a dozen years ago?? - that studio portraits on Portra 160 could be over exposed by 3 or 4 f-stops, and optical prints could be hand balanced to the same color, and the results would be nearly identical. Yet the wedding-shooter lore, and apparently their printed results, is that it gives "dreamy" pastel colors. I always attributed this to problems (or perhaps artistic interpretation) with the scanning process. But now, I wonder if this may have been a bleaching deficiency...
Pps, as a general note to readers, the traditional photofinisher test for bleaching/fixing is to video the film with an infrared scope, in the dark. The film should appear completely blank (the dyes are transparent to IR). If one sees any trace of an image this means that silver has been left behind, but it's not apparent whether it is a bleach or fixer problem. This is answered by both refixing (only) and by rebleaching AND refixing a test sample of the film. If fixer, only, changes the film then you know the fixer is deficient. If the bleach plus fixer shows a change, but the fixer only test did not, then you know that the bleach is deficient.