Is good, works well. 
If you happen to be using IKEA Trådfri lamps, I've had no issues with these running as routers both directly and indirectly connected to my 'non-security' mesh (so long as they remain powered on, obviously). I run two HE hubs now, one fully battery-backed on all devices in the mesh for the security side, then another 'accessories' hub that has all of the lamps, wall switches and stuff that wouldn't work with the power off anyway.
There's a very clever app called HubConnect which allows you to control devices across hubs. In fact, it supports ST, so if you have anything you can't immediately move that may be an option for you.