RE: Foxon's Home Automation Hardware List

Compatibility checklist when adding ZWave devices:

It's manufactured for the same region as your other ZWave devices

Compatibility checklist when adding Zigbee devices:

It's manufactured for the same region as your other Zigbee devices (kind of, there is a lot of play at 2.4Ghz)
Radio: 900Mhz and/or 2.4Ghz are available. 2.4Ghz shares with wifi and is prone to interference. Without interference, you still have a reduced range at 2.4Ghz (higher bandwidth, but that's not usually a need in HA/SH)
Protocol - Zigbee 3.0 is similar to ZWave in interoperability. Anything 3.0 should work with anything else 3.0, and that will only become more common with time. Right now, you need to line up protocols. ZLL devices will not interact with HA devices. SEP is separate from both, but really only used in monitoring

Conclusion

It's not a huge difference, and Zigbee is totally manageable. I appreciate it's more open nature, too. Reliability can be similar depending on which Zigbee protocol and radio is used, but I'd rather just have everything work without having to line those stars up