Well as long as it's not costing you anything, no harm done.
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It depends (TM). App accuracy will vary depending on your mix of lean burn vs. stoichiometric driving. If you're mostly city it'll be closer than if you're mostly highway.
The app has no way to tell when you've dropped into lean burn and your efficiency has gone way up. It (and the ScanGauge & Ultragauge) assumes a stoichiometric A/F ratio only (with some exception for open loop/cold starts, etc.).
I'm not sure how much efficiency improves for the HX when you hit lean burn, but on a 100% highway trip in the Insight (lean burn), it would be off (low) by about 25% by the end.