Although I also have it on the program to fully use my G25, including the clutch, I must admit I did not feel ready for that till now.
Just to be clear, my objective is to drive fast:
1) Mastering slow in, fast out, is still delivering results.
2) Trying different driving lines is still delivering results.
So it is not a priority, but I sure would like to start "soon".
If your objective is to prepare for real cars, just do it simple and slow to start with. You will get the principle but the mechanics of a real car are still different (actually I need to adapt to every different car I drive, but adaptation goes fast with experience).
===================
Edit: actually part of my habit comes from WRS where the cluch is not allowed since it gives unfair advantage on TT.