I've used old school toe clips, half clips, power grips and now Shimano m324's which have platforms on one side and spd's on the other.
[h=1][/h]For commuting I've found that there isn't a tremendous benefit of being locked to the pedal (the increased power is negated by stoplights), but like your concern really like something for when it's a good rain. Your foot slipping off the pedal is a real drag. My conclusions were the two best options were either the half clips http://velo-orange.blogspot.com/2009/12/half-clips.html or the spd's. Powergrips weren't bad. The main downside was that when getting into them didn't work you can't tell by feel what is wrong and have to look down. I would assume that there's a similar problem with the strap you are looking at.

I would go ahead with doing the spd's. There's a bit of a learning curve, but once you get used to them in a week or so there's really no effort that goes into using them. Using the ones with platforms on the other side allows you to still ride in other shoes if you feel like it.

Good luck