Can't speak to the Snoo but my daughter was sleeping like that when she was 4 months. One day I thought I'd see what happened if I didn't respond immediately when she fussed (she was in her room and crib by that point), and she stopped fussing after a minute and went back to sleep. That one night was the extent of her "sleep training". She was just a great baby. It was glorious until she hit 4 and started waking us up nightly with terrible nightmares...

I did at 5 months or so despite having a good sleeper like you, OP. I wanted that consistent 12h stretch vs. just 8-9h (which is still great!)

Yep just see how the transition goes. Mine was an amazing newborn in the Snoo then rocky ish 4 month regression (got almost impossible to put him down at night without a few false starts and started waking again a few times). Then we transitioned to crib at 5 months and he got nearly impossible to transfer back after 12/1am wakes. So we sleep trained him but it was super easy and took one bad night and a few more bad bedtimes. I credit the ease to the Snoo bc he had been sleeping through the night in that thing previously but who knows really.