Couple reasons I like the factory computers with custom Harness:
1) Least expensive even with custom harness etc.
4) Aftermarket tuners - There are hundreds of tuning shops available that are very familiar with Gen3 Hemi tuning
I am simply going to respond to a couple of points that you made above that are particularly problematic.
1) Flat out wrong. The absolute cheapest method to transplant a Gen III Hemi into classic Mopar is to Carb it. The second cheapest is MS2, the Third Cheapest is MS 3. Your solution isn't much cheaper than the FAST setup.
Using your own website it becomes clear that your system isn't cheaper.
According to your own advertisement the cost for a complete kit, plug and play is $2749.00 Then if you read the advertisement carefully you recommend a Diablo Tuner for an additional $400.00 to $600.00.
The combined price above makes your system MORE expensive than the FAST setup.
4) Yes, there are lots of people familiar to tuning Gen III hemi's but am I able to create a custom tune with the Diablo hand-held tuner? The answer is no. I am dependent upon custom tunes provided by black box artists. To me this is the greatest weakness of the Diablo solution. I want to be able to sit at a laptop and do my own analysis of my tune. Right now that simply isn't possible with the Diablo. If and its a big IF, HP Tuners ever gets their stuff together and offers a laptop tuning solution than this might be moot.