It turns out there is also a Smart Tools Mini from the same app developer. The full version costs $4.50, the Mini version is $3.50. I decided to try the mini version -- good choice. None of the Smart Tools apps from this developer are available on my 7" Samsung Tab A2 -- almost certainly because it's too old and the Android version can't be updated to anything near current.
So I switched to a somewhat newer 8" Samsung Tab A. The made the Smart Tools apps from this developer available. My needs/wants are modest and this was an experiment, so I opted to cheap out and install the Mini version. What I found is that the protractor works and can be set for roof pitch (x:12), as well as degrees, so it can be useful for checking framing as well as for ramps slopes (which is what I'm most likely to use it for). It has a decibel meter -- I already have two decibel meter apps, neither of which appears to be accurate, and I don't think this one is any better.
The Mini also includes a lux meter. Light level readings in lux are not easily useful, because you have to convert to footcandles, but it's better than nothing. However, on the Tab A the lux meter doesn't work. It reports a sensor is missing. Not helpful, as it doesn't say what sensor is missing, so I have no idea what I should be looking for if I wanted to upgrade to a newer tablet (which I don't).
So basically I paid $3.50 for a level app that reads directly in units of roof pitch.