Only have used them a few times, and only in the winter time. (When I used to have one car, the Supra, I had studded snow tires on RAV4 steel rims, and summer tires on the sawblades... then my MK4TT rims..)
They work great on snow and ice build up. (Seriously a problem when your driving in weather that is just cold enough to freeze everything in the air flow, but the ground is warm, so the road is wet. Your car quickly builds up a coating of ice, and even your lamps get glazed over.) The only thing that would be better is to run a coil of coolant fed copper tubing in the washer tank to pre-heat the fluid. That would rock on ice and snow.
(My A8 has this, and I love it, cleans ice off the windshield, and the power washers/squirters work great on that car like they do on the Supra.)
I wonder how many people have two cars with headlight squirters? LOL (My Dad has a S500 Merc with wipers, and they are cool too, but can collect ice in the wrong conditions.
I've been on trips where everything on my car is coated with an inch of ice or more. It get's to the point where you have to stop every hour or so and chip all the ice off the upper edge of the windshield, and head lamps. On my work car, ice coated the antenna to the point where it was about 4" in diameter.. :0