If that was your only option… I am right there with you…But if you have a local shop that specializes in Mustangs… I say a custom tune better than a canned tune any day of the week, but not in your case…
If I was spending the money on a custom high-hp build you can bet I am getting a custom tune with plenty of datalogs to make everything perfect. As far as common bolt-ons, unless the local shop is a nationally known 5.0 tuner like JPC, Lund, AED, so on, I would bet the remote tuners would be more reliable.
Might I ask why the extensions that came with the Kooks headers are not recommended?
Too many people have damaged or destroyed their entire engine because the connections between the extension and the O2 sensor itself were not 100%. Regardless, they are not even necessary as the factory harness will work.