Open hand striking is very effective, I have used them too. Its the equivalent of hitting someone with a thick phone book, its stuns severely but leaves no marks. It can easily fracture facial bones and cause nerve damage.
As for litigation , it looks like your just pushing a guy in the face. And you can use the time tested statement..." He attacked me and I threw my hands out to defend myself and he fell over...."
I was told to phrase my statements like this by a police officer at a station after an event.