The GL-AXT1800 Slate AX (and I think all GL.iNet routers) have Samba for sharing USB drives and microSD cards (on some routers).
You can access a USB hard drive directly in Windows Explorer with no additional software vs. having to install Netgear ReadyShare software (but that also provides http and ftp access). You can also backup photos and videos from iPhone (I do not have iPhone, but it works with my iPad).
You can stream videos and music on a USB drive over DLNA via VLC or other DLNA-compliant iOS app.
I do not work for and I am not directly associated with GL.iNet