I had really good experiences with the Interphone F4. Intercom was 100% reliable up to 100 yards or so, batteries lasted a full day with the intercom in alomst permanent use, connection to the Zumo worked fine. When one of the F4s broke, I "upgraded" to a pair of the newer F5s which support multiple headsets paired up, not just a couple, but I've not been so impressed with the F5. But the F4 was very good. I'd buy them again if I needed new Bluetooth headsets.