Have 20% film on our current boat and also had the same on our 04 X30. Really love the look. With that being said, it does hamper your vision through the windshield, especially during low light hours such as early and late. If you have concerns I would go with 35% (light, and legal on most cars) or 20% which is darker but not as dark as the 5% (typically called limo tint).
If I recall, I paid close to 300.00 to have it done both times. Be selective when choosing a
tint shop. Try to make sure they have the facility to do it indoors, because debris in the air or dust can make or break a tint job. The guys that did our X30 did it outside and there were dirt spots all in the tint (dirt shows up as white specks). The guy that did our X45 did it indoors. It looks better. Another MAJOR concern should be daylight showing around the edges. This happens when the film is not trimmed close enough to the rubber gasket holding the glass in. Both our boats have it. Some say that they can do the tint job without daylight showing around the edges, I have my reservations so you probably could expect some light showing. On our X30 the guys used a thin vinyl striping tape around all the edges on the outer side of the windshield in an effort to block the light spots from showing from the inside. On the X45 there is no vinyl tape but there are still light cracks that show. Also verify that they WILL NOT trim away the gasket on the inside in an effort to make the edge of the film slide up under the gasket not allowing daylight to show, I think this could affect the integrity of the glass being sealed in. Also make sure that the guys have done boats before. The extreme curve in the class is VERY diffucult to get the tint to conform to. They will use heat guns and in some cases a butane blow torch to heat the film and glass.
One last thing. In both cases it took the guys at least 5 hours to do the job. The second guy claimed to have done all kinds of boats and promised me the boat in 3 hours. However it took closer to 6. When asking him about why it took so long he said the windshield on a MC was curved more than most boats. Heck I don't know. I can tell you that your black X1 will look great if you decide to do it. Sorry for rambling on.
08 X45 LY6