Its easy...it does get you some nice features in a small package. Other wise you have to tote your laptop around and a tractrix cable every where you go. While a AP can store away in your center console or glove compartment easily. You can be like Josh and have it hooked up 24/7 lol. Is it necessary to have? No, not everyone will like it or want it. But, its your personal opinion and your money. I own one and love it. Especially the last time I was breaking in my engine. God, I'd have a CEL about every 5 mins that I could just clear with my AP, turn my engine off at a convienant place, turn it back on, and drive for quite a while until it came back on. It turns out the front O2 sensor crapped out also, but it was a lot easier to carry a AP around then a laptop.
Edit: Your assumptions are correct. A protuned AP map is much better than a base or off the shelf map (OTS).
378awhp/373wtq Custom Dom 3 & CBRD tuned 2006 STI.
"When in doubt...flat out" - Colin McRae