The one I found for cheap perfectly works with two Tamron adaptalls. Focus to infinity for both and both allows light measurement.
It's one thing to work; another to work perfectly. Perfectly means it works like the original. The knock-offs are not the same; they are very limited. And the adapter would have to be outright defective if it did not focus to infinity.
I have an older Adaptall lens I bought 35 years ago which would allow metering in stop-down mode with one of those knock-offs, if I didn't mind sliding the manual/auto diaphragm switch to M to meter and to shoot at the desired aperture. It would work, but not as well as with the genuine adapter, which allows open-aperture metering and auto diaphragm.
A quick look at the genuine adapters on that page and the cheap knock-offs shows that the cheap ones only physically adapt. The cheap adapters all lack the mechanisms necessary to convey aperture information to the body and actuate the diaphragm. It is obvious by looking at the pictures. On the genuine adapters those mechanisms are clearly visible; on the knock-offs they are obviously missing. The only Tamron lenses with which those mechanisms are not needed are mirror lenses.
The problems with adapters is mainly related for to the ones that change the focal flange distance. For instance, some adapters are used for mounting M42 lenses on K mount bodies, and in some cases, the adapters modifies the flange focal distance and then the focus to infinity is not possible.
Completely irrelevant. That's a different type of adapter. Those adapters allow mounting
fixed-mount lenses onto bodies with a different type of mount. With rare exception (e.g., a Fuji-made M42 to Fuji X-mount) those adapters also eliminate all interaction between lens and body except for physical mounting.
Adaptall, Adaptall II, Adaptamatic, T, T4, TX, and others, are
interchangeable-mount lenses with proprietary adapters which allow them to mount onto a variety of camera makes. They do not have flange distance issues. The knock-offs only would if they were not made right.
So far, the Tamron adaptall system is basically designed to fit every system.
Most, not all. But some adapters are very hard to find now.