Quality! Everything William painter brought to the table from my first (and not last) pair of glasses was precision and quality. First noted when I was unboxing my Level Titainium glasses and then opening the hard protective case as well.
The lenses themselves are fantastic for long use where lesser brands or quality can blue my vision or cause discomfort.
I used these in all types of activity and never once felt that they would or could fall off my head with their quoted rear weighted but also noted that they were so comfortable I will often forget that Im wearing them. I arguably lost them for 10 minutes until I found them on my forehead lol
The biggest issue I have had with these is deciding who wears them better me or her so Im thinking a second pair will be the answer to that issue.

The only thing I would like to see different in the future from WP is to throw in a soft case as well (bag) understanding that it will offer minimal protection but would be ideal for weight sensitive adventures like hiking/camping etc.