There's no reason to go manual tensioner IMO, but plenty of draw backs (you will find that much harder to fit than an auto tensioner - it's tighter unless you modify it (see nafes post for pics) and you need to recheck the tension after a while (strip all the casing down again).
When he said the original one died, it will be because he didn't know what he was doing - it's meant to extend (violently

) when you remove it and you have to wind it back and secure with a bracket to hold it closed. He probably didn't know, or have the bracket.
But yep, agree with the others, you wont be able to adjust one of those cams without having the covers off.
I managed it on the bb4 (ended up same situation as this first time I assembled)

I think I did it by slipping the belt all the way to the edge on both Cam pulleys, the water pump and tensioner pulleys and was then able to just slip it loose on one cam pulley enough to rotate it with a socket on the pulley Bolt, then slide the belt back over everything.