We had those bladders in late 1967, but even the one on e-Bay didn't look like the ones I remember. As I recall, they were a clear plastic. I don't really remember what the cover looked like. I prefered the plastic or metal canteens. It's been 45 years though so I can't be sure. It looks like it was sold anyway.
You're right Rolando they were clear and square prior to this type coming in. The new ones as above were tested in late 66 but the clear ones were still in use in 67/68 but they were replaced as they were found to be too noisy and they split too easy also the clear ones had no pile insulation on the cover.