So far I've seen both great successes using the plastic bottles, and a few downsides to the idea.
...The seedlings are protected from cutworms, mice, rats, and other pests.
...The seedlings thrive and grow rapidly.
...It's easy the water the seedlings, getting the water to stay with the seedlings rather than running off.
...On brilliant sunny days, certain veggies fry. Most of the celery seedlings succumbed.
...On days of full sun, the seedlings dry out, thus require daily watering.
...Regardless of lots of sun or mostly cloudy, seedlings need watering at least every other day. Some needed watering every day.
...Some seedlings grew so rapidly that they were weak stemmed, flopping over when the bottles were removed.
I suspect that the trick will be in the timing. Just how long do I keep the bottles on a particular veggie? 3-5 days? A week? 10 days? I'm going to need to watch and get a feel for it.
One thing I saw was that once the bottles were removed, some plants got killed or damaged by cutworms. Funny thing though, the rodents ignored the older, larger seedlings. That's a plus. So I have a plan to stymy the cutworms. That's my next blog post.