That is total salesman b.s. They've done studies that seem to show that even the pro's don't actually pull up and gain any efficiency. It's still quit debated, but I've switched between clipless and a good flat pedal with a decent shoe ("bare" shoes, any shoe that doesn't compress in the sole is best) and I don't get any noticeably speed improvement from clipless. It's debateable whether it's there somewhere, but it's definitely not 5-15 minutes over a 25 miles ride. I'm definitely faster since I started exercising with squats, though. :-)

The drawback of those "one side clipless, one side flat" pedals is that they're annoying to use when you're getting on and off the pedal - like at stoplights or intersections. With 2 sided pedals you learn to clip in or out (likewise if you're use 2 sided flat pedals) without even looking down. You start to go through the intersection with your head up looking around at the traffic. With those pedals that are different on each side, you have to look down, then sometimes flip it over with your foot. Right at the time when you should have your head up for traffic. It drove me nuts, I'd rather ride with 2 sided flats than have 1 sided clipless.

I didn't find clipless helped me "enjoy" riding more - personally I had to go through several shoes, insoles, cleat adjustments to find a way to ride without them causing knee/foot pain/numbness. Something that wasn't an issue with flat pedals. I'm debating whether to try again on my fast roadie with clipless and a wider shoe, or just throw in the towel and go with flats. Regarding commuting speed, keep in mind that any efficiency you gain with clipless might well be offset by additional time to change shoes on each end.

P.S. Right now on my commuter, I just use decent $40 flat pedals (WELLGO Alloy BMX Mountain Bike Pedals Sealed 9/16") with pins.