This thing is definitely a game changer. The surf adapter by itself is awesome, but the rail gives it a much more fluid motion when pumping. I swapped the 2 cones for barrels (hard), and that gave it just the right amount of stiffness.
I've got the surf and rail on a Taurus (Waterborne and wide AF) deck, and was able to get my ride height down to 5" (deck to ground). I had to ditch the FIN adapter because both settings, Pump and Carve, were causing wheel bite. Despite this, the original non-FIN configuration still works great!
Warning: Choose your trucks wisely. I went through 3 different sets before landing on one that was fully compatible with the surf and rail. Avoid Sidewinder II's, they are fucking awesome with the adapter but good god, you can damn-near taste Earth's lower atmosphere they ride so high. Really fun for flats, awful on a hill. Gullwing chargers work great, but also add to your ride height and are kinda bulky. I ended up using a basic, cheap set of Krown trucks (RKP), and they work great. The trucks really don't matter once you've installed the full fin and rail system, either way you'll be cranking down the kingpin nut pretty tight. Just use a cheap pair of longboard trucks and you'll be fine.