I've only had the S705 for 2 days, but have been happy with it so far. I picked it up new for $20 - it's definately a great buy at that price point.
I haven't used other bluetooth headphone gear before, so have nothing to compare to but I've been reasonably happy with the music quality (wasn't expecting anything too fantastic, and it was better than I originally thought it would be). I'm using my own headphones and haven't tried the supplied ones yet.
Range is fantastic - left the phone on my desk and went for a walk to the back yard - streaming music was still clear without any dropouts (it's about 13-14 metres through two solid brick walls).
Have only made a couple of calls, and after adjusting where I had placed the unit (was using the neckstrap - I had to adjust it a little so it wasn't hanging so far down) I haven't had any complaints about the quality/volume of the call.
Still determining the battery length as I haven't used it enough yet.
I wish it displayed the track name that was currently playing on the display, but I can live without that feature (caller ID is displayed when a call comes through).
FM radio works well - it's built into the unit so you don't need to pair the device with anything to listen to FM.
Hope this helps!