I have 2 ISY devices in two physical locations. Both have Insteon and z-Wave, Aeon repeaters, Kwickset locks, garage door controls and Honeywell thermostats. Since the new z-wave firmware, April 2014, I have not had any significant problems with the units. All have performed without any significant problems. A key to using the devices is to first understand exactly how they respond, with that knowledge in hand the programing is straight forward logic.
Each time I have added a new , to me, device I implement programs that report all events via a notify email for the device. This gives mea good understanding of the sequence of events the device implements. It also is good for debugging if you have a program problem. When done I just disable the diagnostic programs so they are there if I need them. Not all devices are created equal and/or have the same software levels.