I just bought a old 435 and discovered it has a JB4 fitted to it. Up until a few days ago I new nothing about it.
I think this maybe one of the better choices as you can do so much more than just a normal tune. So for example it has 5 different settings for maps which includes one "pro tuning" map.
You can also do things like change the fuel guage to a bosst guage after certain revs or open the exhaust flap permanently or run at standard map, a "stage" 1 or "stage" 2 map depending on your mods. I have no idea on costs but expect it will be more expensive than the normal dynoing.
So far I have only driven to Durban and back and a few times to work but I am very happy with it. (only had it two weeks)
As a side note, i also got Bimmercode and have coded some nice features, like auto stop to be always off unless selecting eco mode or actually pressing the button, changed the displays, switching off the i-drive when opening the door and some other minor changes - im still learning.
From what I can see it is also not coded to one vehicle so if anyone wants to do some coding to their vehicles, let me know. (i work in Midrand and Live in Lonehill)