We just finished a great week in Marathon at this home with two families, including four kids. We had a great time. The kids were in the pool for at least 3 hours each day. It really is in a great location, away from the highway and commercial area, and a quick walk to the beach. There is a well-lit walking trail right in front of the house that is so convenient. We enjoyed the easy access to grocery stores and restaurants. Marathon itself seemed clean and neat, without being pretentious. It had just the right amount of laid-back "island" feel without being run-down and trashy. I think we picked the best key for our first Keys trip. The home was cozy, clean, and well decorated and had everything we needed. Only a few items that you might hope to have: The bathrooms are all upstairs from the pool level, so plan accordingly - however, there is an outdoor shower/rinse down area. Beach towels are not included, so for your beach trips you'll need to bring your own. It would have been nice to have some fishing tackle onsite, especially for the kids.
The management company was great to work with - promptly answering emails and phone calls and even checking in during the week to be sure everything was going well. I believe this property is for sale, so I just hope it's still available for rent the next time we make it to Marathon (and that can't be too soon).