Not long ago, I mentioned a device I came across (which I couldn't remember the name of) that let you measure a device's PWM output. It turns out it was the ECDMeter, but the guy who was making them in Australia (Stoney) doesn't seem to be making/selling them any more, at least as far as I can tell. That device can measure just about everything you'd want to know on your output (ohms, RMS Power, AVG Power, etc...).
At any rate, I did come across another device called "The Omnitester" that measures the PWM output voltage. It's made by SMOK, and although It's nowhere near as robust as the ECDMeter, the cost is very reasonable at about 20 bucks (about the same as the basic 510 ohm meters that are available). This device says it measure atty ohms and output voltage (including PWM output voltage). It includes both a male and female 510 connector on the unit which allows you to test your device output under load (you can vape with your topper and device connected if you choose to). It only shows output measurements to one decimal point, so if more accuracy is desired, it isn't capable (sub-ohm'ers obviously won't like the ohm-meter on this). I've read that the center post may need to be pulled occasionally if it doesn't make good contact (a 510 adapter would probably solve that problem).
Based on a quick search, Madvapes and a few other vape sites carry them for around 20 bucks (give or take). There are also several YouTube video reviews out there if anyone is interested.
@AndriaD: I came across this
ECF thread where you posted that you bought one of these a few months ago. Any additional comments/complaints you could share regarding this device?