The problem I would think with any such meter is that unless you’re just running a constant tone the number would be changing all the time and so unreadable.
Thus you need an averaging of some sort…and this probably starts leading back to an RMS meter.
The one with (I think) the most useful readouts is a free one from TBProAudio (dpMeter5). It has various modes but one is RMS which it gives three different versions of (Momentary, integrated and max). Not sure if it’s what you want or if the display is big enough but the closest I can think of off-hand.
Good luck and do let us know if you find something!