I've had replacement lenses for a Dye Invision, Vforce Shield/Vantage and for assorted JT goggles (nVader, Proteus, Flex, etc.). The invision replacement lenses are really the only ones that compare to the mirrored lenses for the Profiler.
I shoot a 2K5'd GZ, Excalibur, FL Viking, Texas Storm, Ripper, Ripper 2 and Ripper 3 Intimidators. I run a Halo or an Empire Reloader B (and now a Pulse) with a PMI Pure Energy or Crossfire Tank.
Easy to replace, reduce glare, relatively cheap.
They do scratch, can't clean the inside.
I've used many masks and replacement lenses over the years. I've stuck with the Profiler for the last 3 or so years now due to it's quality and durability. I switched to the mirror lenses in 2004/2005 due to the glare reduction that they provide. I've been very impressed with the product overall.
While they do scratch over time, they're no more prone to it than any other lens on the market. I play every weekend and these lenses have lasted several months in many cases. They are incredibly good and keeping the glare down (about the same as the Dye Invision replacement lenses) and are easy to install (unlike the Invision or Proteus lenses).
Cleaning the outside of the lens is straightforward. It's best done with a bit of water (spray bottle) or goggle cleaner and a microfiber cloth to prevent scratching. In a pinch I use a soft cloth with no ill effects. The only issue is the inside of the lens. The lenses aren't true thermal lenses which are double paned. These have a thermal treating on the inside of the lens that is incredibly good at preventing fogging. However, if you wipe the inside of the lens you're likely to tear away at that coating, which in turn enables it to fog. The best remedy is to dip the lens in water and let it air dry. This in turn will minimize damage to the coating and clean the lens. Still though, the ease with which you can take the lens off for cleaning makes for an easy clean up.
Fantastic aftermarket lens. The cost isn't too pricey (compared to similar lenses for other masks). Replacement is easy and the benefits such as reduced glare are amazing.