my typical usecase is that i have a spinning motor running at constant speed (hopefully)(typically turnigy), that i may control with odrive (and then i just want a quick and dirty way to check that it spins as i beleive it does). sometimes it’s with another controller (and here i dont have a clue). and sometimes it’s not even a brushless motor.
ideally i woudlnt connect anything mecanically. dont have to use/configure an oscilloscope.
Last time I needed a tachometer but didn’t have one, I used a laser + LED (as crappy photo-diode) + oscilloscope.
I don’t think this is a good suggestion for your situation, but I just wanted to share ;D.
I have one of those handhelds. There ok. If you can spare $70 a better option is an Eagle tree elogger V4. You get real time or data logging/graphs at 50hz sample rate for rpm, temp, amps/volts/watts and more. I mainly bought mine for rc aircraft but have used it more on non rc related things. Good bang for the buck