Foot blocks are pretty controversial. I can understand the suspension. I used to go for them all the time until I played in a tournament in Maine and they told me the BUDA league banned them because people kept getting broken bones in their hand. Oops I should point out I'm talking about ultimate frisbee here. In ultimate you have a lot of low releases when you're throwing with the forearm and it's natural to use the foot and if you bring the foot out really quickly it's unexpected and sometimes you can get a good block when you're marking people. But then you are so close that it's easy to kick the hand of the thrower... so it's controversial like I said. Basically I chilled off using my feet - especially doing the move where you bring it out unexpectedly. That's where it gets dicey I think. If your foot is already up and someone runs into it or throws the ball into it then it's on them. if you bring your foot up lightning quick and contact their body --- I think that's poor sportsmanship and worthy of a suspension.
I rewatch the clip of Tony Allen and it's pretty obvious Tony had his leg up before Chris Paul got there. Paul was looking away however and moving full steam. It was like Tony clothes-lined him with his foot. That's a dirty play. It might have made sense in his head before Paul got moving and before Tony made the motion, but then as it happened I'm sure both players realized it was a big mistake!
I suppose if it was really malicious he would have had a larger suspension because clearly it was just a brief lack in judgement but with good intentions I'm sure. The fact that both players have talked and come to good terms with each other reinforces that. And makes the suspension seem a little dubious.