I am using them. I really like them. Very easy to use. Cheap and you do not need to be a programmer to know how make them work.
I found this video before I bought the system and phones. They have been working great for me over mesh.
Another brand to consider is Yealink, http://www.yealink.com They also are configurable via web and tftp as well as other means. I've seen them sold on Amazon singly and it blocks of 6 which drop the price down. I've also compared the handset audio with Grandstream. The Grandstream handset sounds a little tinny compared to the Yealink.
I found this video before I bought the system and phones. They have been working great for me over mesh.
https://www.youtube.com/watch?v=U_Y5bSbrFd4
Great basic setup video.
Just my $0.02 ....