Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Excellent for new balls but dont expect to reinvigorate old ones

I bought this with the understanding that it would make my old balls be like new, However, this was not the case it would add pressure to the old balls but they would lose it after a few hits. Not recommended for old balls but I did try using it on a canister of new balls that were just played and the Tennis ball saver kept them fresh for about a week now. I have been using the same new balls about twelve times now and they still feel like new thanks to the tennis ball saver. Recommended for tennis players who want to save money on balls.