I am a reformed garage door installer...it's been 18 years, but who's counting
There are advantages and disadvantages to this type of opener.
- they are best used on a door that has 1 panel still vertical in the tracks. Which erases about 90 % of residential applications. The reason this is important is that with 1 panel still vertical the lift cables on the bottom door section will still have weight on them. A standard residential door will have all panels horizontal. An opener of this type will slack the cables on the drums before the door naturally wants to move. This can create a very unsafe condition where the door will freefall until the cables wrap tightly against the torsion shaft. Of course they will never reach the same point and the door will either jam in a very crooked position and the rollers will fall out and sections will fall on your prized Porsche....or the cables will snap and your door freefalls crushing anything beneath it.
Guys, I have seen it a million times during the decade I spent installing and repairing garage doors.
On the plus side they are quiet and do not take up extra room in the garage. Of course a properly installed opener should never be below any part of the open door.
There you have it, my two cents....and I am not trying to sell you anything
P.S. Never, never under ANY circumstances try to repair or install something that deals with the springs unless you are trained to do so. I have seen way too many Do-It-Yourselfers that are maimed for life from thinking that they could save a buck and work on the springs and related components. It just ain't worth it.