I bought these to use with my synth setup and with my Keytar. They provide great freedom on stage where I have used them a few times already without any issues (playing on up to medium sized stages).
The issues I have had, has mainly been with the app that you use to do the inital setup with. Where connecting them with your phone can be tricky sometimes.
One thing I have noticed is that when powering the WIDI master with certain devices (such as my audio interface) has made it easier to connect, whereas when they are connected to my Keytar they time out in the app.
So try a few different midi devices to power the WIDI master with if you get connection issues. They connect instantly with other widi masters but you will need the phone connection at least once to do the firmware update (which they need to work reliably!).
App issues aside, I already own 3 of them now, and I have been pretty satisfied with them as they have proved to be reliable on stage.