Horizontal dropouts and track ends work the same way, and you don't need a tensioner if you know what you are doing. Horizontal dropouts typically require fewer brake adjustments (if you are running a rear brake) when you change the position where the wheel is bolted (eg: changing ratio and thus changing chain length) because the pad contacts the rim in nearly the same place. Also, removing a wheel with a fender installed is much easier when you have horizontal dropouts. This is why I will eventually be ordering my custom single speed frame with horizontal dropouts instead of track ends.

Even with very little drivetrain wear, a magic ratio will lose its tension rather quickly.

Some chain tensioners either give too much tension or not enough in certain circumstances. I was trying to setup a bike with vertical dropouts and a chain tensioner, and eventually had to change gear ratios in order for the tensioner to find a sweet spot. Pushing down, not enough teeth were engaged and pushing up caused the chain the bind. This was the Surly chain tensioner. Some people might say that a chain tensioner doesn't look as good.

Also, you're probably not going to find the answer you're looking for in this thread, either.