Agreed, but can you elaborate on your FL 040 sentence? Surely the narrow route brief goes higher?
Yes sure it does, I was just making the point that for an average (!) GA triangle trip, say to a waypoint then landing at another airfield then back home you can define a (say) 10nm route up to FL40 max with precision. ALL other non-relevant stuff is filtered out.
It does work well for VFR flying with some room still for improvement!
I also like the FREE UKGA graphical tool - interesting to cross refer with AIS.