>>1505527without horizontal fork ends (track ends) your gearing options are severely limited
as the length of chain and thus its tension is set almost entirely by the size of the chain wheel
and semi horizontal drops outs only really allow a few teeth worth of tension adjustment either way
for the purposes of making a single speed bike a mono directional chain tensioner is fine
they are very easy to find and attach directly to the derailleur hanger
for a fixed gear bi directional chain tension is important even if you dont plan on rely entirely on back pressure on the pedals to slow the bike
very few exist and are mostly for industrial applications .eg ROSTA Tensioner and Roll Ring
