This is a great kit, with clear instructions and the brackets are beautifully made with powder coated metal. But reaching the spare optical bay isn't something for the faint-of-heart. Essentially, you have to disassemble your Mac Pro down to the logic board, removing
1. Memory cards 2. Two sets of screws at the memory card cage 3. Video card 4. All disk drives and sleds 5. Screw that attaches the processor cage (for which you'll need a long-tang'd Phead driver) 6. Fan cage 7. Optical bay, itself
I got as far as #5 before reflecting on how hard it would be, potentially, to reattach that piece, when I left off.
This is, of course, not OWC's fault. It was an Apple design decision that this part of the box didn't need easy access that causes the problem.
I'd rate this 5 if it were a bit more obvious on the item description what is involved in using the part.