Just go with the handheld for now. You won't see any crazy gains with it, about 10 hp at the peak - the advertised gains of 20+ hp such as Bama uses as their selling point are lower in the rpm range, like from 3000-5000rpm. It will wake your car up and make the trans shifting a bit more aggressive, and as you continue down the path of modding your car (stuff like gears and intake/exhaust mods) you can have changes made in the tune file to accomodate.
Dyno tuning, I would save that for more advanced things like power adder or heads/cams. And in which case, your handheld device will be used by the dyno tuner to upload the new files to your car.
2001 ***** Slayer Red GT convertible; all of the usual bolt-ons.
1967 Notch; 200 I-6, C4 auto