Doing the tensioner isn't hard, but requires more effort than just replacing the serpentine belt and idler. You have to take a bunch of stuff apart, including disconnecting the alternator and removing small timing belt covers. I don't think it is a big deal, but if you aren't much into wrenching, you may not enjoy it. I did the idler on mine when I did the belt/tensioner. It is a couple of minute job if you already have the belt off. If the bearings are fine, it is a waste of money to replace it, but mine were rough, and it is hard to tell until you have it off the car, and at that point you are stuck if you don't have the replacement part handy.