No, I would never use them. I don't want my soil littered with synthetic pieces of Oasis. If I'm growing something that doesn't like transplanting I use newspaper pots that I make. Then I can plant the whole thing and the paper will rot down to soil.

Making paper pots is easy. Find a jar or dowel something that has a flat bottom. I use a piece of broom handle cut flat and level so my pot sits straight. Measure the height you want your pot and 3/4 of the way across the bottom. Now cut strips of the black pages of the newspaper the width of your measurement and long enough to go twice around your dowel. Once you have the strips cut the rest is easy. Immerse your strip in a tub of warm water and lay it flat on a table. Put your dowel or bottle on one end and roll it around twice. On the bottom fold in the paper like you would a coin wrapper. Carefully lift it off the dowel and set aside on a flat surface to dry. Fill with a good well draining soilless mix. I put them in a tray, plant the seed and leave them there until I plant them out

I've used newspaper pots before- those are fun!

However, I quickly had trouble with all sorts of mold- a few sprouted little mushrooms. Granted, it's more my luck- no matter how hard I scrub things down, mold happens. :)

I can understand not wanting synthetic materials in your soil, though; it's one of the reasons I avoid rockwool.

Oasis cubes aren't for outside use, as they are made from foam. If you want something for outside, you can use rockwool, but newspaper pots or peat pellets would be better.
using dirt in a starter tray is popular too!