My first really useful mod was the AP. With it I learned that bone stock 2500-6500 rpm pull took 8.6 sec. Added Mountune intake and 2J DP, no difference. What?
Learned to use Vdyno, graphs confirmed AP raw data, no difference. Old news now but startling to me in early 2014. Duh. Tune needs to match hardware.
I weigh my car and know diameter of my running gear. Always note temp and barometric pressure and wind. Now have close to 100 Vdyno runs from stock to C39, fall 2013 to present.
For me, there is no reason to get a "real" dyno. The only real data I care about are PB's at tracks. And since I use Harry's LT, that is not "real" either, just close enough for my purposes.
Vdyno is easy to misuse. Many users do not realize it offers three different presentations, one Mustang simulation, one Dyno Jet simulation, and one real calculation that is probably more accurate than the other two. What do see on this forum? The one that reads the highest.