I have been on geni since dec 2009. Since then I have been fortunate to locate a number of relatives, including those whom are related by blood and by marriage. I have also located a number of inlaws.
Be aware that the person in charge of the family tree may not be your relative. They could be a distant inlaw. I have found researcher attitudes to be varied. Some are actually indifferent, some want to just copy all of my names, and a few are actually interested in engaging in a discussion on research.
Researchers can accept new researchers as friends, family group, or collaborators. Friends can see your tree but cannot amend it. Collaborators can amend your tree.
One has the option of allowing complete access, limited access, or no access to unverified geni researchers.
Cost - the basic tree is free. Pro version allows for gedcom and amending information. There is a monthly charge.
Pros - a webpage that will accept a gedcom file and create an instant tree.
Cons - the inability to update gedcom files. the ability of collaborators (whom you have accepted) to amend your tree.
Privacy - one can set the levels of access. It is a good feature which will allow you to hide info on living people. One can limit the access to verified relatives, registered geni users, or anyone on the web.
My verdict - For 100% control over names and profile info, you may want to consider avoiding the "collaborator" option. The "friend" option will give interested researchers 100% access to your tree info w/o the ability to amend anything.
I paid for a pro account. I suggest that users play it safe and just accept people as "friends". As I want to encourage people to look at my tree, I have my tree privacy set to open view for anyone within geni.