I don’t remember reading that, but it could have slipped past me. Do you remember where you saw that?
I saw that the glowforge warranty would cover any damage to the machine caused by proofgrade materials (which makes sense, as they are formulating those materials themselves and actually have control over what goes into them), and I would imagine that covers the filter too.
I have not seen any specifics of what the filter cannot handle. I did see @dan mention that people should only use laser-approved materials from trusted sources. He recommends Proofgrade, of course, but also mentioned some of the other established names that sell laser-safe materials to the public, such as inventables. Surely there is a similar supplier in the UK? (If not… business op!!)
Considering that people want to put these into schools, hospitals, homes, etc… the filter had better work pretty darn well, or come with some serious warning stickers.
Personally, I would never equate what is done commercially with what is safe… especially in terms of emissions!
You could very well be right about that, which would be a bummer.
On the flip side, maybe there will be a bulk importer and it would be an option.