The Zyxel P312 router is a unit with tremendous flexibility and so far it has been completely reliable. Unfortunately, only about half of the setup can be done with the GUI and so you must resort to the Telnet interface for the other half. Outbound access to the internet is excellent and fast. I have experienced no lockups, or failures of any kind in two months of use. Software stability has been superb.
Inbound access is another story.
While P312 is supposed to support inbound access to telnet, http, and lots of other services, there seem to be some problems. While Zyxel tech support tells me that I should be able to set up the firewall to allow telnet access with the firewall active, many hours on the phone have not provided any firewall setup to accomplish this. Even with the firewall disabled, only telnet access to port 23 is possible. Zyxel is supposedly working on these problems, but I have had the unit for about 6 weeks so far and they have not produced a firmware upgrade to address these problems.