The basic point you want to tell him is that these tensioners are not like the old spring/oil pressure ones .
These have a ratchet device that , as the chain wear/streaches. the tensioner ratchet locks at each step it extends.
The reason for this is that the old ones would leak pressure if the car sat for a while , and then when you started the engine , there would be too much slack until the oil pressure pushed the tension back onto the chain.. The ratchet locks the tensioner in its last extended position and it can not go back [..so, if you put in a new chain or do a repair, you have to take the tensioner apart , pull the rod out past the locks and re-install it from the back side so it starts off anew.
Otherwise, just putting the tensioner back in a cranking the bolts down will put extreme tension on the chain and cam , as the tensioner is preset to the LAST locked setting.

Here is a link that has a couple of points on BOTH styles , and this may help you if you can print it out.

Can't install timing chain