Drawtite, Hidden Hitch, and Reese hitches for the Focus are identical products (with Reese being available at the lowest price point of those 3). Curt is the lowest priced all around, but requires drilling of the frame rails.
I went with Reese and installed at home. For my heat shields, I simply snipped them and folded the specified sections out of the way. Have an angle grinder or belt sander ready for trimming the bolt heads that go inside the frame rails (they are just a bit too large to fit inside the holes of the frame). Have a friend help support the side you aren't working on! Very self explanatory once you get into it.
From what I gathered, 1,000lbs is the recommended limit.