A bit leftfield and you may, not unreasonably, hate the idea, but I’m using a Forward Components external eccentric botton bracket thing on my old Setavento hardtail.Bolts on and allows you to use a HT2 crank-set.
Clean rear end, easy enough to fit and adjust, doesn’t slip, hasn’t creaked so far despite me being a little dubious about it. Means you can singlespeed a geared hardtail frame without some godawful tensioner at the back and if you want to swap back to gears, just take it off again.
I ran a Voodoo Wanga with sliding tensioner things for ages and I prefer the Forward Components thing. Gives you a much wider choice of off the peg frames as well.
Anyway, just a thought.