Here's my painful 'growth' so far:
1) Bought an Echowell U4W wireless bike computer
2) Bought a Polar FT4 Heart Rate Monitor Watch
3) Sold the watch. Bought a Polar H7 heart rate monitor (paired with iPhone)
4) Bought a Wahoo cadence/speed sensor (paired with iPhone)
5) Sold both sensors. Bought an Edge 510 performance bundle (I'm still using the Echowell unit as it's tiny/inconspicuous and performance is faultless)
Main reason for this upgrade is that I need to see real-time HR & cadence info; can't really do that with iPhone due to battery issue.