I am seeking an inexpensive "travel modem" (small, lightweight),
Requirements:
Wireless connectivity: The modem needs to be able to connect to and negotiate wireless logins common in hotels and other public spaces. Needs to negotiate the splash/login page. I presume this can be done by connection of computer directly followed by MAC cloning by the modem.
Needs to be able to negotiate connection to VPN (I use IPVanish).
Preferably, power should be via USB/micro USB to allow usage of external batteries to charge phones.
Torrent capability to a connected drive would be helpful.
I already have a GL.inet GL-AR300M modem; perhaps this will already work? I cannot see how to wireless connect to a wifi connection to web.
The AR-300M should be able to handle all or most of that, within the capabilities of a single-core MIPS processor. Leaving aside running additional services ("torrent capability"), the functionality should all be possible. Either the travelmate package or the GL.iNet OEM packaging should make configuration and operation in a typical travel-router configuration a lot easier. There is some complexity around running a client and an AP on the same radio at the same time that these packages help manage.
Battery operation for any router will be limited by the fact that running the radio and the Ethernet consume significant power (figure ~300-500 mA for consumption at 5 V). A 6000 mA pack might run for ~10 hours, given that I suspect that the figures quoted are "optimistic". A good 18650 cell has about 2 Ah of capacity before falling below 3.5 V and those packs look like they've got two cells in them.
Running additional services on the router will load the CPU and increase drain. There is also the power required for the USB stick. Past that, the security concerns suggest to me that the torrent server/client be run on a machine that is within your network, rather than on your router.
I have multiple power options and the power requirements can be met, thanks for the excellent review on this topic that I had not considered.
The AR-300M is new to me but I cannot torrent under a VPN yet either through the AR-300M or another VPN access.
Although I threw in my total wishlist, the most important part is the wireless connection (which you note is an issue running as a client and AP simultaneously).
Are you aware of a travel (or other) modem that had two radios or another way to create a VPN access point in a hotel off their wifi?
I'm pretty happy with my AR-750S "Slate". It's compact, lightweight, and has the advantage of 5 GHz wireless over the AR/MT-300 units. It runs off 5 V through a microUSB connector. I can check the power consumption later this evening if you want.
My only complaint about the unit is that there is an acknowledged bug in the uboot that has restricted me from building my own images for it, as it won't connect in uboot recovery to macOS, Linux, or FreeBSD machines. The bug does not restrict its use when running OpenWrt (or the OEM OpenWrt build) from what I can tell, only if I "brick" the thing and need to access it through uboot.