These ANT+ sensors (HR included) have an amazing range. Tested the signal up to 27 paces (+70ft) away which obviously means these are fine for even the longest of tandems.
Unfortunately, yesterday the speed sensor part (cadence & speed are combined) on our tandem failed in mid-ride. Likely this was the previous root issue I mentioned where our speed had dropped out. Cadence keeps working and the sensor is reported as connected. Doing a rescan while riding brought back the speed for a diminishing amount of time until it never did come back at all. Alas, Amazon to replace it for free. The speed/cadence sensor on my single has a lot more miles and is still rock solid.
The Edge setup is really nice with no wires and only needing one spd/cad sensor. Can have multiple HR belts and head units, no kooky interference values. Much better than our old Polar setup. I'm sure the stoker might prefer a iPhone w/GPS app, but letting her talk on the phone or texting while we ride is a deal breaker for me. Dual Edge 800s are the limit.
I've opted for these $17 Control Center mounts instead of Barflys, etc:
http://www.amazon.com/gp/product/B00...ls_o03_s00_i00
The key benefits are to allow the Edge tilt to be easily adjusted while riding (as sunlight changes), to place the front unit further forward in the line of sight instead of directly down (bad - rider not watching the road), and the two bar attachements eliminate vibration (a frequently reported problem people complain about with single arm mounts). Having the correct view angle is the difference between a dark, barely readable screen vs. one that is bright and easy to read without dropping your head to see it.
This last weekend I used my 800 to nav a 112 mile preset route (.gpx) in a local GranFondo. The event organizers provided a near 1MB track file on MapMyRide which I downloaded into Basecamp and converted to a lighter weight Route instead. The turn directions all alerted perfectly. I still need to figure out how to get proximity alerts because none of the Food Stop waypoints I inserted provided any notice. Luckily in this case I knew where those stops were on the course, but in future touring abroad those points will be more unknown onroute.