It's been very interesting reading the posts in this thread regarding transplanting autoflowers. I have transplanted auto's before, but have mostly start auto's in their final pots.
Gone with 4 gallon smart pots from go this time.
For me, the only reason why I think transplanting has a major advantage is you can grow a few extra, take the strongest 4 or whatever number you need. Several times I have started auto's in their final pots, 4 in each tent and only 3 germinated. That's a royal pain in the arse! As you end up with 1 plant 4 days behind the others and it usually got swallowed under a otherwise level canopy.
So now I have 2 litre / about 1/2 gallon smart pots for next time. So I'm going to grow a bunch of them, give them 7-10 days in the small smart pots, then just plant little smart pot in to a bigger smart pot. I think that would be a great way of not stressing it out, whilst getting the benefits of some early air pruning.