Espruino Wifi with Adafruit Ultimate GPS - no data

I've got an Espruino Wifi, and a Adafruit Ultimate GPS (https://www.adafruit.com/product/746).

I've got the following code from the tutorials;

Serial1.setup(9600, {tx: B6, rx: B7});

function onInit() {
  var gps = require("GPS").connect(Serial1, function (data) {
    console.log(data);
  });
}

onInit();

The GPS module appears to power up ok, it's red LED flashing once every 1 seconds for a satellite fix, however i'm getting absolutely nothing back from the console.log. Not an error, not a success, nothing.

Not really sure where to go for troubleshooting from here. I believe I've got the pins wired up correctly.

Is it simply that the GPS module provided won't work "out of the box" with this module, do i need to do some lower level interfacing? Or perhaps something else is afoot?

Is there generally any way to debug/troubleshoot in circumstances like this?

EDIT: just to note: experienced JS dev, completely inexperienced Espruino/Ardunio etc dev!