I've used standard rollers for decades and can ride them in my sleep. When I first started, i set them up in a door frame, which made it easier to start and stop, plus kept me on them since my shoulder would hit before the tire ran off the end of the rollers.

However, with some experience I learned that you ride where you look so would watch TV while riding and never have a worry. As a added measure of safety I glued sandpaper strips to the ends as sort of a rumble strip in case I was getting too close, but it didn't make a difference. Once you get used to rollers staying centered is as unconscious as holding your line on the road, In fact it's easier, since there are no potholes to avoid.

BTW - a big help is to set up a milk box to the side as a step for starting and stopping.