I don't think there is anything wrong with "crowd sourced" photos, to complement your Wedding photos, but the cameras in the above link are frankly.. well.. poo. Most people have a digital camera, iphone or similar and can take snaps to complement your quality pics. Perhaps then just add a basic half day session from a pro and you have a good combination.
A good pro will always flex their service to cater for your needs.
The problem with guests doing the photos, is that they will busily take pics at the beginning and then forget as the day goes on. Also cheaper cameras (anything <£3-400) just can't get enough light in to capture a quality picture in lowerer light, so your evening/indoor pics will be dark and grainy. There is no substitute for pro gear in low light conditions.
[This post was edited by weddingshooter at . ]