The SF4 is a continuation of the SF1 and an extension of the SF2, if you will. Where the SF1 limits itself to all functions such as music, GPS, telephone and intercom function between rider and passenger, the SF2 opts for an intercom function between riders; you can go out in group with the SF4.
Both the Bluetooth functions and a conversation, everything is on point. Up to 1200 meters* away, four people can talk without a problem. The SF4 is operated by voice and with Bluetooth V4.1, a built-in FM radio receiver, stereo sound, electronic wind noise reduction, quick charge system (1.5 hours), about 13 hours talk time and a standby period of seven days, the SF4 again delivers a lot for relatively little money.
In open terrain
In addition to the (smaller) standard speakers (35 mm diameter and 8 mm thick), the HD version also includes larger HD (High Definition) speakers (45 mm diameter and 12 mm thick). The HD speakers give an even better, clearer and louder sound than the standard speakers. When you have limited space in your helmet, you can keep using the standard speakers.
If the SF4 is too much of a good thing, then the SF1 or SF2 might be more your thing. In all three cases, this is a sleek, slim and handy device that should fit in just about any helmet.
General remark: The world of electronics (which also includes intercoms, smartphones, GPS's, etc.) is changing so fast, that it is possible that some (outdated) devices are not compatible with each other in certain areas. Unfortunately, the manufacturer can't provide us with data that shows which combinations between intercoms/GPS's and/or smartphones cause problems. A regular update of all electronic devices is therefore desirable to avoid problems as much as possible.
