I have become a little evangelical on the subject of Speedplay pedals. I'll try to explain why.
1. When I worked in a 'bricks 'n mortar' store I had the joy of learning about bike fitting. Frankly it was one of the most enjoyable things I ever did/learnt. What you could give to a customer at the end if a session was more than worth the £ notes they'd spend. So for me the first important thing about the Zero series pedal is fit & the options you have to tune the riders position. Front, back adjustment are catered for much in the same way as any other pedal. But having independant float adjustment from internal & external rotation is where the set up goes into another level. Spring tension & release angle are not effected by the float adjustment.
2. Commuting in London I always longed for the user friendliness of a double sided pedal when coming away from the lights. But if you have used any road pedal switching to an MTB you can feel the reduced contact patch. This is not welcome. What is great with Speedplay is that you get both a wide platform (don't let the small pedal body fool you, the cleat engulfes the pedal & unlike some comes in contact with the whole pedal body) and it is double sided. This can only be done by turning conventional thinking on it's head. Putting the adjustement into cleat means that the pedal itself only has one real moving part, the axle. This allowed Richard of Speedplay to swap conventional thinking around and make it double sided.
3. I love the way the pedal feels because of all the attributes I have mentioned above. I used to suffer badly with a tight IT Band. No matter how much stretching the problem didn't go away. With my stretching regime combined with the pedals I have not suffered since. Also those riders with dodgy knees have benefitted greatly by switching, myself included.
Okay to the negatives. There are a couple, but for me not deal breakers.
4. Cost for many is a real hurdle to overcome on trying them. Due to the fact that they are made in the States & not in the Far East means that the costs will always be higher. In principal the pedal is the same across the whole Zero range, it's just the axle that changes. I've always had Stainless Steel, but I've been sent a Cromo pair to see if there is a noteable difference. Once I've logged some kilometres on them I'll write a review.
5. The main issue is with cleat wear. The brass plate can scratch & look worn quickly if you happen to do any walking on them. This does not effect how the cleat engages the pedal. The other thing that annoys me is that because of the open nature of the Phillips cross head screw it can become worn & difficult to remove. Cleat covers make a lot of sense especially since cleats cost £40+. Speedplay reckons you'll get 2000 miles out of them. In practice depending on how you look after them it can be more or less. In my experience it has been more. I wish there was some clever cleat cover that covered the exposed heads but at the same time aloud you to engage the pedal.
So to all those people who've asked the question I hope it's answered some of your questions.