I do have one and is useful but I wouldn't trust the reading for anything but rough guess. Identify a part, like those old packages you can't tell what it is just by looking at it, check if a cap is still a cap, etc. And it also generates pwm signals to test a few things around. Usrful yes, metrology garbage also yes. It might get lucky once in a while or even more often than not but trusting it's reading would come to bite you eventually. A friend was trying to measure a guitar mic coil and it just reads resistance, a frikking coil of wire around some iron and it reads resistance! The error is also you usually can't force the thing to read a choosen model, so it reads what it think it is.
Sig gen scope gets you a long way to characterize an impedance but not so much for a precise value reading if you try to match components, for that you should use a bridge, to get a good value a bridge with a reference component. Or if you are doing it a lot get a proper LCR meter but the coice of freq and amplitude is usually limited, with sig gen and external components you control every parameter of the test and can get more meaningful numbers for a given application, even if less precise than a proper meter.
JS