Accuracy of 60Hhz power measurement device on 50Hz AC

I picked up a wallplug measurement device kind of like a WattsUp. It
appears to be an excess from China/Hongkong source, the "junk" shop
had just this one piece. But I grabbed it because I've seen nothing
like this sold locally (we don't charge for PF so nobody cares) and
everything else from the net only seems to be designed for 115VAC.

Now naturally with items of such origins, the instructions and
specifications can be vague/unclear. One section says it works from
57Hz to 63hz, one part says it won't work with anything outside of a
85~250VAC 60Hz area, yet the label on the actual unit says 50/60Hz.

It appears to work on my local 230/50Hz, the frequency function shows
49.8Hz so it seems that at least the frequency measurement component
isn't having a fit.

But the question is therefore, if the device is actually designed only
to work within 57~63hz but tolerates working at 50Hz, would it still
be accurate or would the readings for PF or VA be off by say 20%?

If it would be inaccurate by a certain factor, how do I calculate the
actual values of VA or PF from the displayed readings? TIA!

--
A Lost Angel, fallen from heaven
Lost in dreams, Lost in aspirations,
Lost to the world, Lost to myself
.