Solar cell power output comparison without MPPT
That is a reasonable way of doing it.

You could also just measure the current with an ammeter - they have a small resistor and measure the voltage across it, just like you are proposing.

The voltage across the meter is designed to be a maximum of a few hundred millivolts so it should keep it below the point where the current starts dropping off.

It will still work at low light levels but you can change the scale of the meter.

A couple of warnings:

Make sure you keep the leads between the cell and the meter short and of suitable wire thickness or the voltage drop couple exceed the 500mV limit.

This is one of the rare cases where you would connect a current measurement meter directly to a source rather than in series.  Make sure of your connections, with a maximum of 600mV you are unlikely to damage anything though.

Why are you using such a large cell just for measurement? You could use a much smaller, cheaper cell.

You could also use other light sensing measurements but unless they match the spectral sensitivity of the cell they might not be accurate.