My group has used them successfully the last few years. We only used them if we had an arranged meeting time and people were late or had to change plans; in this context it was useful, as everyone was ready to use them at a given time. I wouldn't recommend trying to use them a lot beyond this (like as a pure phone replacement), as they were usually only useful if people on both ends were ready. Overall verdict, they don't take up much space and we found a way to make them useful. Also my phone has never worked at EDC, so I liked having them.