Not a lot in it price wise, except 600 miles of fuel. Both are highly regarded so take your pick. I'd choose the nearest and cheapest option personally.
As for custom vs generic, you will get a wide variety of opinions, but here is mine:
'Fully custom' is an exaggeration when it comes to tuning a car with the usual bolt ons. VW did 90% of the most difficult calibration, which tuners don't touch. It's just minor adjustments, like fine tuning a radio, which I don't consider to be 'fully custom'. i.e. Sony made the radio, you are just tuning it. VW made the original tune, APR, revo, R tech etc just fine tune it.
If you rolled up with your non-running car on a low loader because it has a 4" MAF housing (or a MAF delete), massive turbo, screamer pipe, huge exhaust, different intake manifold, bigger throttle, bigger injectors, different cams etc etc. Getting that to start and run reliably for 10 years in every season is extremely time consuming. Most of what VW did is now irrelevant and has to be redone from scratch. Now that is 'fullly custom', imo
Perfecting a tune behind the scenes and selling multiple copies of it is given the label 'generic' in the scene, and touted as inferior..... usually by people who've never calibrated an engine themselves. Do you reckon these people have a problem with McLaren shipping the 720S with the same generic tune?