Silo's developers have abandoned it. There are unfixed bugs from years ago in there.

I really liked Silo when it was developed and recommened it to others, which I now regret. This is what compels me to post this warning. If you really want to buy it make sure you test it thoroughly because it is unlikely that bugs you find will ever get fixed. The developers are writing iPhone apps now and are just milking the last few $s out of this project.