We bought frogs to go on our new tandem and while my wife finds them great I've had a few problems with them. I bought them so that I would be able to use normal touring shoes as I need to build the cleat for my right shoe up by nearly 10mm. The frogs have a large cleat area that makes this easier to do.
If you have big feet your feet have to be in the right position to be able to unclip or else when you twist your foot hits the crank before the release angle is large enough. Speedplay do make a longer spindle for this reason but you need to read the fine print carefully to even find out that it exists.
So if you take a size 12 or above (mine are 13's) order the long spindle.
Cheers
Geoff