The current/ammeter issue will be similar but is a slightly different kettle of fish.
Virtually all measurements will be of a "chopped" current. Unless you are driving only resistive loads such as incandescent passenger car bulbs, ALL command electronics have bridge rectifiers to convert the AC to DC. So even if the voltage is be pure-sine, the current will be "chopped" though in a slightly different manner than voltage chopping. I can't recall if GRJ has posted current waveform examples but in basic terms no current in drawn when the voltage is near 0 or a few volts. Then you get a spike or pulse of current near the peaks of the voltage.
So averaging analog meters or averaging digital meters (like their voltmeter counterparts) will under-report the "chopped" current drawn by modern engines (with bridge rectifiers).
What I predict will be the conundrum is the current range of interest is, say, 0-10 Amps (wide) where as the voltage range of interest is, say, 14-18V (narrow) and pure-sine for command applications. Attempts to mess with the calibration adjustment on the inexpensive averaging meters may be unsatisfactory if trying to measure over a wide range. Note that this has nothing to do with whether the current/ammeter uses the donut-style current-transformer or a built-in shunt to sense the current.
