I have the 540's and have never had an issue. Easy in and out, rarely ever come out when I don't want to, and not terribly heavy. A fellow MTB'er has the 520's and he said he's gonna upgrade even though there is only a few grams wt difference. If you can find them and they aren't terribly expensive the I'd suggest the 540's any day of the week.

Edit: They will work with any SPD compatible shoe. Make sure you find something that fits your foot well, it's not really something someone can sugges to you. I have Addidas MTB shoes that feel okay but I wouldn't recommend them. Now I'm just too cheap to replace them.