First, Teamer does what it says it does (with a minor glitch here and there) and is a very useful tool for any team leader. So, give it a try.
That said, they are so close to having an outstanding, indispensable app.
For instance they have the "team talk" where you can post discussions. You can choose who receives it which is good, but if someone comments on it, everyone receives an email, and my team rebelled against the email traffic. So, I still use TT, but its mainly used as one-way broadcast tool from me to the team.
They have a nice invite system for events, and people can block out days they are not avail, but as any leader knows, to get people to proactively do something like that is not reliable. They have a "standby" system, but that doesnt take into account positions on a team (that who the replacement is can depend on who is missing). Whats missing is an "availability poll" where you can ask whos avail and then choose a team from there.
All that said, Ive been using the Teamer app/website successfully for about 1 month (with my work-arounds) and its better than trying to do all this with email and txts and google calendar.
Give it a try and see if it works for you and your team. Its definitely worth the time to take a look.