I installed some glass tile on my backsplash and remember that I had to comb the thinset in a horizontal manner so that the trowelmarks wouldn't show through the glass. (Translucent white glass)
Not sure if it's pertinent but thought I would share...
Thanks william, the glass is translucent so i will keep that in mind.
Bud. I guess what i was saying was I didn't think i would be able to trowel a smooth wall since my skills aren't professional grade and as I got close to the lip of the tub it would be even more difficult to keep it clean and off the tub. I am trying to avoid hours of sanding. Since the 1/4" cbu would work I'll go that route. Much easier and faster.