I haven't used that company but in my experience it's not hard to come by an invite and your likely to pay less for the 64g model than you would buying the 16 gig phone from a third party company.
I have been trying all over google+ instagram and the one plus forums and have had no luck getting an invite but i will keep trying.
Have to also consider the radios inside it. There's a version, the Chinese one I think, that apparently doesn't have some LTE bands.
Posted via Android Central App
Taken from expansys website so it has bands for at&t and i think tmobile is the 900mhz but i may be mistaken there.
Connectivity
GSM: 850, 900, 1800, 1900MHz
WCDMA: Bands: 1/2/4/5/8
LTE: Bands: 1/3/4/7/17/38/40
Wi-Fi: Dual-band Wi-Fi (2.4G/5G) 802.11 b/g/n/ac
Bluetooth: Bluetooth 4.0
NFC: 65T (software card emulation, payment methods and multi-tag support)
Positioning: Internal GPS antenna + GLONASS, Digital Compass