I had better luck with pedals that required less heel twist before releasing. Shimano's SPD mountain bike pedals are my current favorite. Walkable shoes, adjustable release tension, and the SH-56 multi-release cleat if you need to make it even easier to unclip. Good stuff! I've never had a problem getting started: shift the bike to the correct gear, clip on foot to a pedal, jump on and start pedaling; SPD can be pedaled pretty effectively even if you're not clipped in.

Of the pedals mentioned by the OP, I've used flats with PowerGrip straps. If the straps are tight enough to provide any benefit and you use a shoe with a lugged sole it can be a bit difficult to get away from the strap. Not quite as bad as a clipless pedal, but close. If you leave the straps loose they don't provide much benefit, but you still have to worry about flipping the pedal right-side up so you're not dragging the straps on the ground as you pedal. If you're worried about falling over, I'd probably skip these and go directly to flats...