A non-True RMS meter can have an error factor of up to 30% on AC systems that include harmonic components in the sine wave.
Personally, I only use True RMS test gear for finding things like stray neutral currents and the like.
I see that APPA has just released a new series of True RMS Clampmeter/Voltmeters
And one of them, the A16R has a 1000A scale
this can be seen at http://www.appatech.com
Having the Cat IV 600V/Cat III 1000V rating's also helps.