I have these and love them. The liquid elastic at the top is nice and has a much better feel than my previous arm warmers. Whether it holds or not over time is another story. But nothing is worse than a warmer with shot elastic.
Living in SoCal I can't say how low these rate down to for temperature. However, I did recently wear these during a morning ride in sub-40F temperatures and I never felt even the slightest bit cold or even cool. So they're good down to at least 35-40F.
Sizing information is impossible to find for this product. Ask any shop. They don't have it. However, Giordana was nice enough to pass the information along.
Hopefully this will help you make your purchase decision. I definitely don't regret mine.
Size - Length - Circ. at top - Circ. at Wrist
M 455 mm 270 mm 170 mm
L 470 mm 290 mm 170 mm
XL 480 mm 300 mm 180 mm
M 18.0in 10.75in 6.75in
L 18.5in 11.50in 6.75in
XL 19.0in 11.80in 7.00in