The new polymer buffers are made by Blackjack buffers/Power custom and they are guaranteed to last 5,000 rounds . The marlin factory buffers were brittle crap and only lasted +/- 1,000 rounds. I have a Camp 9 and it takes S&W 5900/6900 series magazines which is ok cuz you can get 20 rounders for it that work great.The biggest issue with the Marlin camp rifles was the bolt buffer at the rear of the receiver. It was made of plastic and would crack with heavy loads and usage. I'm surprised that no one hasn't machined a replacement out of urethane because it's alot more durable.
The second issue, (IIRC), is that they were only compatible with certain 9mm S&W mags, and nobody had come up with the idea of the magwell adapter yet