Chain tensioners collect as much dirt as derailleurs and need cleaning out. They are a kludge for selling std hybrid models with IHG systems or a useful way of fitting IHG to your existing bike with vertical dropouts.
My bike has vertical dropouts with eccentric bottom bracket. Its has a twin bolt external clamp which is simple and reliable. Internal wedge systems can stick, the better one as are self unlocking.
Sliding vertical dropouts are good but quite rare. You should also consider a split rear triangle for a belt drive upgrade.