The problem with SleepCycle that I found while I owned an iPhone is that you have to place it under your pillow, and the way that I sleep, I shuffle around a lot and my phone would often fall off the bed and onto the floor, rending the entire thing useless. The Wakemate is a device that you wear on your wrist; eliminating any shuffling/pillow problems.
I'm using SleepCycle until my WakeMate arrives. It's very good, but my problem is that I sleep with my girlfriend, and the iPhone seems to record both our movements. I tried last it last night without my gf sleeping (she's on a trip) and I found the graph to be quite different.
I imagine having WakeMate's wristband will negate anyone else's movements on the same bed, and record just your own.
except that the alarm may disturb your girlfriends sleep pattern as well (I emailed them about this and they were considering adding wristband vibrate functionality in there one day)
I'd buy this thing for the 'wake me silently' alone.