This is somewhat OT, but after using a PowerTap SL+ for the past two years, I cannot see how the Vector offers any serious advantages over a PowerTap. And I'm not shilling BTW. However, here are some reasons why I still think a PT is a much better value than something like the Vector:

1) Time-tested device

2) MUCH cheaper, especially with the new price drop.

3) Compatibility. Let me expand on this:
3a. All one has to do is pull off the freehub body (with little force might I add). So switching between a Shimano/SRAM and Campagnolo bike (for example) takes less than a minute, especially if the freehub bodies have cassettes already on them.
3b. You can easily switch out different freehub bodies for bikes with different gearing. For example, one bike might have an 11-23 cassette and another might have an 12-28 cassette. All you have to do is have a spare freehub body/cassette.
3c. No tools needed. Are you seriously going to take a pedal wrench to swap out pedals between bikes? Swapping wheels is such an instinctual habit in cycling, anyone who has had a rear flat can do it. Removing pedals or cranks is only for those mechanically inclined to do so.

4) Maintenance. It's pretty easy changing out batteries on a PT. All you need is the plastic wrench that comes with the hub and screw off the top, sort of like opening a bottle.