mechanical belt tensioner vs hydraulic

[btmed]

wondering if anyone has had good luck with replacing mechanical belt tensioner with one off ebay, $50, opposed to replacing with hydraulic. Found one that the warehouse is about 11 miles away from me.
Called moritz bmw and they told me they dont make mechanical any more and that the hydraulic will cost about $300in parts. But if i go with hydraulic ill only have to replace the pulley from now on. This is a 2001 x5 3.0 111k miles and im pretty sure its never been changed. I can buy 6 mechanical tensioners for the price of 1 hydraulic. Im also pretty sure my wife wont be driving this thing for another 9 years! and yes ill also be replacing the deflection pulley. both are shot.
anyone used the mechanical replacement?

Thanks BT