The folks at TalkSwitch responded to my query about how they were different. Let me see if I can summarize the email I received:

• Not open source, based on a product that's been in-use since the early 1990s.
• Focused on making it really easy to use.
• Extensions and lines can either be analog or VoIP. "Hybrid" is the term they use.

While that's great talking points, they admitted that the best idea would be for me to have a look at the system for myself. They are going to send me a unit to have a look at. As usual, I'll let you know what I find out.