topping autos is counterproductive to their growth cycle...with a normal strain you top it, then veg it a little longer to heal itself...since an auto doesn't have a controllable vegetation period it will reduce yields if you top it.
not true, it depends on the strain like and your grow environment, like all cannabis. I've done this experiment with EVERY auto i've ever paid for, because i've learned that some auto's respond well to topping/fim in early veg (10 days or earlier) and those that begin flowering at 20-25 days from seed are uneffected by topping/fim. it just makes the plant bushier. Did this to my fruit auto's and it increased yield, while the other half(control group) yielded less, and the bud was less potent. the pineapple express auto's ive grown were negatively impacted by this losing yield but gained potency. Short stuff's Mi5 is better Topped/fim'd and really brings out sidebranching which ups its yield and prolongs flowering period.
extension of flowering period was the main detriment i witnessed from topping an autoflower, as the plants always finished a week or 2 behind the non topped. Try it you may find the results favorable. i think earlier autoflowers were prone to week growth and stress with this method, but the more modern bred strains have less ruderalis traits dominant besides the auto feature.
currently i am growing some autoflower crosses i've bred myself, and i fim'd them down the middle to 50/50 topped/nontopped (each 8-11 days from seed) and its been 3 days and all are responding well to the fim, with new growths already branking out. they were at 3 nodes starting their 4th node and they are almost the same size as those who weren't topped. it may be hybrid vigor that's keeping these so strong or the fact that they are half Dinafem fruit auto and half TGA Jillybean/Chernobyl/Vortex.
