Great question! Glass mosaic tiles are a great use for a backsplash, but definitely not a good use for a wainscot application. The reason why is they tend to get quite expensive, so using it for that application can get costly.

Do you have a picture of your bathroom? Id love to give advise based on the bathroom itself. That would help a lot.

All mosaic tile is much more expensive than field tile, with more difficult install as well.. I would limit this to an accent, and even then be prepared for "dated" up the road. Frankly, I'm sick to death of them. But an accent around the sink, or a swath in the shower. have at it. I'd simply ask, what does it say when you've already said you don't want ........." too much like all the others" : ) I rest my case.............

I'm very tired of glass mosaic tiles. And that's without actually seeing it ever day.
People here often suggest "Get what you love! Who cares if it's trendy or whatever!"
But speaking for myself at least, what I "love" today, I might be thoroughly sick of 5 years from now. I had considered all sorts of "interesting" decorative tiles 15 years ago, when our house was being built. Eventually (mostly cuz I was overwhelmed with the choices) I went for very neutral tiles in all the bathrooms. So glad I did! I'd be hating those decorative tiles for sure by now.

I reread my post and see I was not clear about how I was planning to use the mosaic. Sorry! We have an approx 8 x 10 space for bathroom. Toilet and shower are facing each other sharing end wall. Will build half wall to separate vanity from toilet. Plan is to subway tile starting at half wall around end wall (continuing half wall height, paint above) through shower (full shower will be tiled). Thinking to run the 4 or 5" mosaic through the subway tiled area ( just below the first row of subway) all way around through the shower at same level.

So question is would it be too much to also mosaic inside of 24"L x12"H niche (in shower/tub)? This is where I am concerned about too much mosaic (I also feel there is an overuse at times). Also have the backsplash (vanity) area to consider. This is a modern bathroom primarily white, with darker vanity/tub decking, and mosaic thrown in.

TIA for any suggestion offered.