I had 4 little glass tiles installed in the corners of large tiles on the bathroom floor. They were labor intensive for sure because they weren't the same depth as the other tile. Some of them sank and had to be pulled out and replaced. I think they do come with a different set of problems for installers. Some come with paper on the front. So installers can't really see what they're doing with respect to gauging the mud depth, etc.
The size of the tile and the type of application are the important factors.

For glass tile, that's actually kind of low. You're only looking at about 20.00 a foot. If it were me installing it, it'd be costing you about another 5.00 a foot, minimum.