I won't say it's useless, but there are too many components that can affect the measurement result IMHO. It will need frequent calibration I'm afraid.
There is a better method and that is to mimic many of those LC meters out there already, by using the Shifted Frequency of an oscillator, but this require that you have a frequency counter of some sort available. A counter on a multimeter will work just fine since it is the
difference in frequency we are after, not an accurate one-spot frequency. We then manually calculate the C or L based on the difference. This method is accurate within 1 to 3 percent as long as the Q of the capacitor or inductor is reasonably good.
It is also easy to inject a current through the measured inductor on different frequencies to see whats happening with all those ferrite cores scrounged over the years. Way more flexible!
I have created a simple javascript calculator to use with this circuit but the coding is absolutely horrible and will make me stand out as a complete fool here on this forum
But, I will give it to you if you PM me. I can also help out with a calibrated inductor and/or capacitor (L1, C1) if you need to.