Hi... if I might add a few "cents" worth from this side of the pond....
Denglas UV Clear, TV ConClear and Guardian Inspiration UV are all basic UV filter glasses with no low-reflectance properties - in other words they are 2mm/2.5mm float with UV filtering. All hit good UV numbers well into the 90% plus range (300-380 nanometres). ConClear and Inspiration are made on Guardians "Extra-Clear' float glass. I don't know which substrate Den use for UV Clear. Exta-Clear is a float glass with improved transmission figures and reduced colouration. It is not a true low-iron ("water-white") glass but benefits from some very clever chemistry.
TruVue also use ExtraClear as the substrate for their AR and Museum products.
True low-iron glass (Guardian UltraClear, PPG Starfire/Solarfire and Pilkington Opti-white) are - as many have already stated brilliant, clear, colour-free glasses with very high visible light transmission - and are really great for framing.
Unfortunately, they also transmit a lot more UV than regular (greenish) glass and therein lies the problem. To hit the expected 97%+ UV numbers on regular glass substrate is difficult enough. To do it with low-iron (with up to 20% greater UV transmission) is much harder. The problems are made even worse when low-reflectance (AR) coatings are applied. These multi-layer coatings can reduce reflection of visible light from the 8.5% average for float down to as low as 0.5%. You don't need a math degree to figure out that means 8% more light for a UV filter coat to deal with. So, with a low-iron (water-white) float AND low-reflectance coatings it's almost impossible to hit the high 90's in UV filtering without resorting to laminating.
Thus, Water-White Denglas - that paragon of clarity, true colour rendition and low reflectance only filters some 30-35% UV (300-380nm). Schott's Miroguard is only a bit better and neither are designed or promoted as UV products. However, when laminated they hit 99% UV and retain their optical advantages but at a cost in both $$ and thickness.
In practical terms, which basic UV clear glass you use is down to price and local availabilty/distributor. TruVue's Con Clear seems to have good availability and price but suffers from the heavily rippled coating. Guardians is still in development but is showing great promise with invisible coating and keen pricing. Den is a very nice product and easy to use (cut and instal either way round etc) but is a bit more costly.
For low-reflection(AR), low-colouration(WW) UV glass, it is down to TV Museum with the rippled coating and dull appearance (but at a relatively low price) or a water-white laminate which really hits the spot but is costly and difficult to cut. Schott's lovely 2mm Miroguard Plus hits 82-83% UV and is reasonably priced, but can be a difficult sell due to the low UV number.
The trend here in UK is rapid growth in the use of basic UV glass - where there is only a small extra cost (an easy sell) and for the high-end collectors etc to go for laminated WW/AR where UV is an issue or WWDenglas/Miroguard where UV can be controlled (by filtration, laminated glass in the windows etc).
The speciality picture glass market is growing rapidly and this will surely attract new product developments over the next fer years.