I will guarantee that you WILL encounter issues....If you download a lot of files and feel the need for some form of safe protection, use Clamxav from the App store, free, safe, and totally unnecessary...But just read the post's...Mackeeper will eat your Mac in time...I'd bet on it.
I did have some speed issues but put that down to not having a enough memory but have now upped it to 16gb.
Having now spent the morning reading many threads i am contemplating deleting it, not bothered about a refund not exactly a lot of money.
I have not had any of the issues most people have talked about, the only issue i had was some speed issues.