well, i can't give you specific materials on anything, but i will tell you that i love my Hornell Speedglas 9000X! from everything i've read, self-darkening lenses are totally safe. and they definitely increase productivity because the less you have to raise your helmet to find where your next weld is going to be, the faster the product will be produced. it also reduces neck fatigue because you don't do the typical welder helmet neck flip to drop your helmet in front of your face before you strike the arc nearly as much. and another thing...a lot of welding veterans will tell you this is the easy way out, but i think a self-darkening lens helps a welder find the start of a weld or to stay on target when restarting a bead. if you can't see it, the odds are against you in hitting your mark. if you can see what you're aiming for, chances are you'll hit it just right. and you can get the self-darkening lenses with a variable shade option...usually 9-12...which is great for a welder who works w/ different processes like MIG, TIG, and stick.

now for the cons...they don't work at temperatures under 20 degrees F. they can't even be stored at those temps, or the lens will be ruined. they are pretty durable, but if you do drop it enough times or from a high enough place, the cost of replacement is pretty high. sometimes if you have a tight place to weld in...say a semi-blind corner or something...the light sensors might not pick up the light from the arc and turn on the darkening electronics in the lens...which means you'll have a rather angry welder w/ a temporary blind spot for a few minutes.

all in all...if you have a lot of stop and go welding going on, self-darkening lenses are the way to go!

My two cents....I am the average daily welder that welds ten hour days 6 days a week with an auto darkening welding helmet. I currently have 7 Speedglas lenses from the APC-V, XL and 9000X and 9000V, series. Speedglas has to be the best as far as quality of product and service goes.. I have sent my XL's off to be cleaned, and never been charged once. Hornell also has product loyalty for the 9000 series, where if for some reason the product is out of warranty and the repair cost will be high, they will give you a percentage off the cost of a new one.
Matter of fact Hornell has come out with the FlexView (tm) helmet that allows for the cleaning and preparation of welds and weldments without the typical shade three lens that most autodarkening lenses have. The front lens flips up and out of the way and a roughly4" by 5" lens gives you the visibility to grind and chip. If you're needing hard hat hoods, Hornell makes the FlexView with a Protop(tm) welding hood/hard hat combination. And as far as temperature goes, I've never had a problem welding with any of my Speedglas lenses in temperatures as extreme as -10 F. To the objection of getting flashed, if you're doing low amp tig or maybe even welding partially in the blind, Hornell makes the 9000Xi for that application. Sure the cost may seem a bit steep at first, but the production you gain and the rework and grinding that you substantially cut down on will pay for the hoods many, many times over. If you have any questions, don't hesitate to e-mail me.