I have and love my Shimano 540s. I have used them on my mountain bike mainly, and recently on my commuter. A friend of mine donated his 515s, which nearly killed him, and over 100 angry mtbr. reviewers.
I was wondering if I should just put the 515s on the commuter, as they are more likely to get scraped and beat up, and leave the 540s on the mountain bike, or should I stick with one type of pedal all round?
My concern is that I will be uncomfortable each time I switch to a different bike, and have to do the learning curve all over again. I have never even tried any other pair of clipless, so I can't compare, but I know it took me a while to get used to the 540s.