My old TP-Link MR3420 (HW revision 1.x), although now LTE compatible thanks to DD-WRT, but obviously pushes the hardware side with 16Mbit to its limits, brings with DOWN and when uploading only 16Mbit over the LTE modem.
I can not say anything about the praised in testing wireless part of the RT-N18U, as far as I am not come. So I can only write about my experiences on the LAN port. At least so performance bottlenecks between router and PC are excluded.
It begins with the fact that the existence of Austria is denied simply in the configuration menu for the USB modem.
Fortunately, you can make all the necessary settings manually.
If you understand even that one only has to select UMTS as the technology before the next drop LTE (4G) gets offered, you can make the search for his device in the selection list of the router. Available for 1 year Huawei modem E3276 and E3272 are nowhere, but automatically by setting it will come.
After a reboot (3 min) and again 1 minute waiting period the LTE connection is successfully established. Here before the first rough disappointment: The router has no status display on the Internet via modem. Network operators, technology (GSM / UMTS / LTE), and signal strength (in dBm ideally) should at least be available.
The next disillusionment follows then the Speed Test. During my modem connected directly to the PC 65Mbit download and 23Mbit provides upload, go to the router only 18Mbit DL and UL 9Mbit over the airwaves. In both cases, the modem is of course at the same point, namely at the window on a 3m USB cable. The performance in the download is therefore in the field of in the tooths MR3420 (HW rev. 1.x), and in the upload even much worse.
Another point that should be mentioned:
You can define 2 Internet connections. By default, the primary connection is made to the Internet via the WAN connection (eg DSL / Cable), and the USB modem is used only if the WAN fails or is simply not infected. Here, the USB modem will also work. But if you now the USB modem defined as primary, or even switches to SingleWAN with USB modem, is not so funny. Either the modem is no connection, or it connects, DNS works, but no data is simply transferred.