What I don’t quite grasp yet I guess is this taproot on these autoflower. When you say transplanting after only 10 days from germ. Don’t you find the medium doesn’t stay together nicely because there’s not enough of a root structure
So I'm fairly new to autos as well but I've run a bunch so far this season and here's my observations on transplanting.
A lot of people transfer around 10 days simply to err on the side of caution. The taproot on an auto grows straight down much quicker then on a photo and when it bottoms out it can cause the plant to flower much earlier than you would want. But this issue is really most problematic in really small containers, like 4" pots and solo cups. In a 1 gallon container you should be able to go longer before transplanting. I'm actually kind of experimenting with this right now. I have a couple autos that are going outside in 3 weeks so they will need to stay in their one gallon pots until then. We'll see how it goes.
That being said, yes, when you transplant the medium likely will fall apart a but. For autos it really should. If you ride it out until the roots fill the container like you often do with photos you run the risk of it flowering early either from the rap root bottoming out or transplant shock.
But as you can see from the other replies, lots of people keep their autos in 1 gallon pots all the way through with no issue, so if you start in a pot that size you don't have much to worry about.