Shimano Deore RD-M5100 1x11 as a tensioner in the low-budget Slopeduro project

Hey everyone. I've recently started assembling a slopeduro bike from random parts I've been putting aside, trying to keep my budget as low as possible. Unfortunately, I don't have a dedicated singlespeed chain tensioner, so I'm planning to use my old Shimano Deore RD-M5100 1x11, but I'm not sure if that's a good idea, as I've heard that chain tensioner can be fickle. What do you think?