I picked up one of these when in the USA a couple of week ago. The MS stores in the malls only stock the 7" one so I asked them to get the 8" one specially and collected it a couple of days later.

Very impressed, you have to set the device up from WiFi, so it downloaded about 400Mb while in the hotel, once all the updates were done you can then enable the 200Mb per month for life T-Mobile. The T-Mobile SIM was already installed and the remaining sprue was in the package.

Although it is a signature device, you still have to be careful during very first use as the first request for email/password comes from an HP device registration, skip that and then you go to the normal Windows credentials for your device's primary account.

It does indeed have a GPS, it will also use WiFi and mobile also for location. The way to tell if it is using GPS is to use the "GPS Satellite" program from the app store, if it shows your altitude then it is using the GPS. While on an overground train it was happily able to track my journey.

The device is offering to reserve a Windows 10 update, so that must be all part of the MS plan, might be time to add an SD card then.

I also confirmed USB devices work with an OTG adapter.