Is that the system where vertical lines are threaded through grommets in the sail? Kind of like a suspension bridge cabling?
If so (even if not) what was the cost? Any downside or inconveniences?
Yes. Here's a link from Doyle Sailmakers on the system.
Doyle Sailmakers: Dutchman
Main disadvantage is that removing the main in the fall and installing in the spring is a bit more involved. The special topping lift wire with the monofilament lines must be removed and coiled. When I priced a new main last year, I got a quote of $800 to install a Dutchman system from North.