But that still sort of begs my question...it's all well and good to know that I'm 700' AGL at that moment in time, but what I really need to know is what altitude AGL I'll be at in the near future, and since the terrain can change (sometimes dramatically) in a short distance, I can be quite safely 700' (or whatever your requirement is) right *now*, and considerably below that in just a few seconds or minutes.
And regulatory is one thing, but using it for terrain avoidance is even worse, I think. Imagine flying around the western U.S., and thinking you're safe because your *current* AGL is 1000' above the ground. There are zillions of places where the ground will rise up sharply in just a few short miles and smite thee.
I guess I'd say...learn what 500' or 700' or 2000' looks like, and then use an actual aviation chart (available on SV) to select your altitudes accordingly. YMMV, but I'd prefer not to fly along watching a constantly-changing number to make sure I'm legal or safe