I'd say 4 maximum.
Not too much work to SCROG, you won't be waiting forever till they fill the screens and the screen space per plant will be enough for it to actually work.
Top tip: Don't use a screen with big holes and make sure it's pulled as tight as possible.
If the screen has big holes the plants will be floppy and you won't get an even canopy.
If the screen isn't pulled tight enough the strength of the plants growing will just push it up also fucking up the canopy.
PVC/Vinyl covered fencing mesh is the best stuff to use.
The stiffer the better.
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