I recently replaced the drive belt for the second time, at about 178,000 miles. I found it easier not to lock the tensioner in position with a drill bit or similar. It's quite fiddly to get the new belt around all the pulleys especially as it is still quite stiff. Being able to easily apply and remove the tension makes it easier to go around each pulley in turn and move the belt across so the ribs in the belt sit in the correct grooves in the pulley.
The original factory belt was replaced at about 110,000 miles, after the dealer commented on the fine cracking in the belt. I kept this belt to carry as an emergency spare. I replaced it with a Continental belt, but after another 68,000 miles, it was in a much worse condition that the original belt, with wider cracks and chunks missing from the ribs. The new belt is Dayco, hopefully it will outlast the car.