OK I'll try this.
There are basically two types of tile adhesive. The first one is THINSET and is a portland cement based product with some additives. It comes unmodified and modified and each has its own particular uses. That's the first type.
Then the second type is organic adhesive or what is normally referred to as mastic.
Mastic is fine to use in dry areas. In wet areas such as a shower mastic is no longer a wise choice. I say "no longer" because the mastics of today are not the mastics of yesterday. When the V.O.C.'s where removed from products mastic tile adhesive and its ability to perform crashed significantly.
Now the manufacturers of this product will insist their product is suitable for showers. This is because they all want their products to be all things to all people. The truth is the mastics are known to reimulsify under wet conditions. Mastics depend on a typical tile installation to shed water and keep the mastic dry. This isn't always the case since no tile and grout installation is waterproof and water certainly will penetrate through the grout over time. This is also why drywall is never never never to be used for shower walls and this is why a moisture barrier is required over the studs and behind the wallboard.
Also pros prefer thinset because it can be used to fill and build if necessary and moisture or even water saturation will have no effect on it what-so-ever which is something you could never say about mastic. The "pre-mixed thinsets" today are nothing more than mastics with a little sand added to simulate real thinset. Some of the manufacturers have gone as far as to add gray coloring to make people think they are the same product, they are not the same in any way and coloring them gray is basically dishonest at best.
In Bob-ettes case her project is very interesting but I doubt any of the tile will stay on the wall after water is sprayed on the huge grout joints on a regular basis if premixed thinset was used.
The same thing goes for the pre-mixed grouts. They aren't working. We see many complaints weekly about these premixed thinset and grout products. The premixed grouts shrink and pit terribly when used in larger grout joints and they cause a surface skim on the tile that is hard if not impossible to clean off.
Seems that in this fast-food-world we live in these days everyone wants quick everyone wants easy and the manufacturers of the tile industry are quick to comply even though the products don't work. I promise you....the use of any premixed thinset or grout will not result in a Happy Meal. You could well be eating your project in a few months.
By the way.....glass mosaics are again becoming very popular and even the use of glass marbles has appeal to some people. Mastic is never recommended for applying any glass tile products to any surfaces. All makers of glass tile offer recommendations for adhering their products to a substrate and none of them suggest the use of anything but modified thinset.