My birthday is coming up on April 1. I would love to get a speedlight or some sort of off camera flash. I have no experience with off camera flashes. I have a nikon D40. I found a SB-400 AF speedlight on amazon for 129.00. Is that a good deal? I also found a SB-600 speedlight flash on amazon for about 190.00. Is that worth the extra money? What am I looking for in a flash? Can these flashes also do a strobe effect?