you know, I have a car torque wrench, but I dont think Ive ever used it to torque down a cassette to X ft lbs, and to be honest, I dont keep track of how many clicks I go to, but it must be 5 or 6 or something--so yes, I would have to do some experiementing to see if what I find is an acceptable tightness would work with one of these removers that brace up against part of the frame.
Typically I think 40 NM is recommended. That is about 30 foot pounds. If you don't pull more than about 30 pounds on the end of a 12" wrench you won't have any problem. I probably go on the light side when installing cassettes, but I have removed cassettes that were factory installed and had been on for a long time and cassettes that were installed by other people (including pros) to unknown tightness using the Unior tool and I never had a problem.
My point is that I think the tool's limitations are not that much of a worry other than to say it probably is a good idea to not over tighten your cassette (a good idea in any case). I don't think it is a case of needing to under tighten it or really worry about it at all. If you want to I am pretty sure you could tighten it to the proper torque an have no problems if you use the tool properly. To that end, I'd advise watching the video and doing a dry run or two to get the procedure down.