Theory, albeit very interesting and informative , and practice are 2 different things
I use el cheapo chinese lenses in my "mainstream" machines , they do the job VERY well , they are ZnSE lenses.
I recently bought 10 lenses for $300 , LESS than the $350 GCC agents wanted for just 1 !!!!
Undoubtedly the better lenses DO work slightly better especially for cutting , but when running 8 lasers and having staff that are less than meticulous when cleaning lenses (despite training) , it is an economic decision as we treat lenses as "consumables"
In general laser engraving , the detail you get from these lenses is as good as any customer wants or needs , small spot sizes are a double edged sword too , especially when doing fills or large area solid engraving.
Rodney Gold, Toker Bros trophies, Cape Town , South Africa :
Roland 2300 rotary . 3 x ISEL's ..1m x 500mm CnC .
Tekcel 1200x2400 router , 900 x 600 60w Shenui laser , 1200 x 800 80w Reci tube Shenhui Laser
6 x longtai lasers 400x600 60w , 1 x longtai 20w fiber
2x Gravo manual engravers , Roland 540 large format printer/cutter. CLTT setup
1600mm hot and cold laminator , 3x Dopag resin dispensers , sandblasting setup, acid etcher