I thought the info said it covers an acre. That said, the research I performed showed that heighth was also important. Place higher than 7 feet. Haven't had it long enough to see if it works on deer/horse flies.
This is my first time using them. We just put them up. I would have to say NO since the sticky stuff you spray catches the bugs and really doesn't wipe off. Once the balls are full I think you just throw them away?
This is the first season I have used them. They work great. I have reapplied the spray only once to the ball that I have hanging next to my pool, so I would say they are reusable. I have not tried to wash it, so cannot answer that question, yet.