I have had very best results with it. No additives required. 90 grams of dry substrate (in blocks) yields 1 Liter of substrate ready to use. But it is rather expensive.

Thank you so much Hans and Donna! Great to hear that this stuff is useful and gives good or even better than just good results. I will experiment with it for sure and hopefully with seeds from some of my own crosses...
Although Hippeastrums will stay as my number one fancy I am interested in clivias also and will be ordering few in the near future. Wonder if clivias would like this stuff too? If the plants arrive potted I won't disturb them but if I get bare root then it's a different story.

The medium was on discount and now I'm thinking if I should get some more...

I can usually find coir at plant sales, however, I have not been successful when using it - in other words, for my climate I am more successful with my other mix (potting soil, sand, pearlite and sometimes grit). However, I keep coconut fibers on hand to use when using net pots to keep the soil contained - this allows for excellent drainage. I am not sure why the coir doesn't work for me, I suspect, like Donna mentioned that it holds too much water. I also found it difficult to monitor as the top seemed to dry out while the substrata is still moist.
Hans, do you find it holds water longer?

I still use substrate from Cococnut husks above an equally thick layer of SERAMIS, for sowing my Hippeastrums. "propagating-amaryllis-from-seed" provides

Thanks for the link. I read that years ago but got more from reading it today then I did them - I guess because I am actually trying my hand at propagating with seed:) I'm growing some species from seed and wanted to be able to transplant easily I like your method and will try it on a couple of the crosses I'm trying with Papilio and Papilio hybrids (your pictures and Donna's tempted me in this direction) . However, with the species I wanted to transplant into separate pots so that when they grew I could up pot easily. I used hydroponic net pots that I lined with coconut fiber to keep the soil from draining out (the long fiber used in hanging pots) and added soil with added granite (grit) and pearlite for drainage and placed the seedlings in their net pots into the containers that you use so I could water from the bottom. It takes more room but that's not a problem as I can grow outside. What do you think?
Anyway, in keeping with the generous nature of the forum members, I will keep you updated with my success or failure in this experiment.