Yea, that said, I would run a roller over a tensioner any day of the week.
We've never used a tensioner and run our bikes from +8-14. And we use and have more suspension travel than most people.
Then he must assume people are going to use a chain tensioner. That bottom roller is a must. When the swingarm is all the way down the chain will rub the frame without it. I'm just warning you now before you have your frame PCed.
Top or bottom? If you have suspension travel you better have the lower roller or you're going to have problems.
Arlo runs drag bikes so he would have no use for either. There's no suspension travel on his bikes.