Making tiles from polymer clay IS so easy; I've NOT used them for outside mosaics because I don't know about their stability and I don't know how they would stand up to grout (if used). That question might have been asked at one time but I'm not sure we came to any conclusions. Maybe querying one of the companies that makes it could help?
Haven't tried the reverse method of mosaicing either--then there is the double reverse!

I have never made the polymer tiles but I have tried to use some...the ones I used did not stand up to grouting at all..I was very disappointed. I'm sure it could just be how these were made so you'll just have to try.

I have used the reverse method several times...it works great as long as you do NOT need to see the top side of the glass, such as if you want to use a glass or tile that has a pattern on it, you cannot see it to tell if you like how it looks together. If the tile looks the same on each side (front versus back) it works great and they are all level when you get it done so if the tile is of different thickness it works out well with the reverse method. Hope this makes sense!!!