I threw an acrylic on a 209 build and it didn't seem to have any melting issues, although I only used it for about a minute. Same thing with a 2.3w m140, I wanted to see the dot difference between a g2 and acrylic. Turned it on for about 30 seconds, probably ridiculously stupid but fortunately nothing happened.
Earlier in this convo I wanted to go to a source of these number claims and asked DTR about the percentage numbers and exactly what lenses are being talked about.
From DTR- "The G-2 will give 25% over the three element lens with blue and 30% with 405nm. Don't have exact numbers but it is something like 15% over an acrylic but the acrylic can only be used with lasers under 200mW or they melt and really under 100mW if you never want to replace them but they are a single element lens and do have fairly good pass specially if you find the AR coated ones which I don't see often."