Probably not the thread to start this discussion, but IMO starting autoflowers in anything other than their final container is a fools errand. Yes they take up less space, but they never get close to their full potential with even a single transplant. I've started hundreds of seeds and 62 autos over the past 6 months and every plant that was transferred is doing, or did, far worse than the non-transplant counterparts. Doesn't matter if I used rooter plugs, solo cups, larger plastic cups, if I wait till the tap root is visible, or not, every plant that was transferred has done relatively poorly. Yes, you can still get them to grow and flower, but you're ensuring a bad start and a significantly smaller yield, though if there's any positive they do finish 1-2 weeks faster with the stress.