I love ET-S clearomizer for its capacity, but I have a big issue with very thin windows. It's impossible to see the liquid level without turning on a bright light, and I've burned the coil more than once. I started with K1 to quit smoking then moved on to more serious mods, but I still love K1 and use many of them while checking the taste of the e-liquid. ET-S vapes just as perfectly as K1, and I seriously wish Aspire would get rid of the sleeve to make it all clear like all other tanks and clearomizer. It really is a good clearomizer to recommend to smokers without having to fill as often as K1. Please do consider getting rid of the sleeve.