[Mondial]

One thing to be careful of is input loading. The counter has a MOSFET front end and a pair of back to back protection diodes from input to ground, so if the signal is more than 0.7 v peak the diodes will conduct and load the measured circuit. Better to add a series resistor to reduce signal if it is at high level as in a tube osc circuit.

Actually, the time base is very good. It has a TCXO designed for use in cellphones, rated at 2.5 PPM.  Amazing the quality of mass produced parts these days. Better specs than expensive counters of a few years ago, and all for $9 including shipping!