Local conditions
The door is open eight months of the year
The Door Stays Open, The Blind Stays Quiet
The reason panel glides sell here and not everywhere is the same reason verticals do: this coast builds around the wide sliding door. The difference is what happens when that door is open, which around here is most of the year. Vertical louvres swing and knock against each other in a through-breeze. Flat panels on a track do not.
The second thing is salt and dust on the track itself. Within a few streets of the water a bottom-running track collects grit and the panels start to drag; a well-specified top-hung system avoids most of that. It is worth asking which you are being quoted, because the price difference is real and so is the difference in five years.
And a panel glide needs somewhere to stack. On a door with a wall to one side that is easy. On a door with glass both sides it is the whole problem, and it is better solved with a tape measure at the quote than with an apology at the fit.