On a quick search, I couldn’t find a detailed manual for this app. It is relatively young but quickly found a larger community and is evolving. Here are just the changes for the latest version: Call for testing - Deck 0.5 Beta
There are probably no software limits regarding the number of users, so feel free to test it a bit yourself and report issues if you find some. I hope a few more advances users of the deck app can give you a bit more details.