This router began life as a T-Mobile TM-AC1900 and has been successfully converted to Asus RT-AC68U. It is running the latest stable ASUSWRT-Merlin firmware for enhanced performance, stability, and advanced features. The unit has been tested for several days and is working reliably.

Key Features:
Model: Asus RT-AC68U (converted from TM-AC1900)
Firmware: ASUSWRT-Merlin
Dual-band Wi-Fi: 2.4 GHz + 5 GHz
AiMesh support (can be used in mesh networks)
WPA2-Personal security enabled
USB 3.0 and 2.0 ports for file sharing, printers, or 4G/3G modem
DLNA Media Server support (stream photos, videos, and music to compatible devices)
Advanced features: VPN support, Adaptive QoS, AiProtection, Traffic Analyzer, Guest Wi-Fi

Performance (tested):
5 GHz: ~244 Mbps download / 11 Mbps upload
2.4 GHz: ~50 Mbps download / 11 Mbps upload
Latency: ~15 ms (Miami server)

This unit has been reset to default settings and you will be presented with a configuration wizard upon login
Username: admin | Password: admin. 
You will be prompted to change the password

Condition:
Used, in good working order. Fully reset and ready for a new owner. 
Screenshots of the Merlin interface and speed tests are included for reference.