I'm an NEU rep and went through the checklist with my head at the end of July. It took a couple of hours, though a number of points were left unticked, as you would expect in such a lengthy document. It's not a legally binding document and it won't affect the reopening as others have stated.
Some posters are talking as if when the union wants something, it must happen and if not schools won't open. In reality, if heads won't agree to points (or agree to them and then go back on them...) there's not a lot that can actually happen, unless members are minded to make a big deal out of it, which none of them are ime, me included.
The point about vulnerable staff is that the union would support them in asking to work from home if they want to, but many actually want to go back to school. Again, if someone does want to work from home and head refuses, the union doesn't sweep in and force it to happen.
The NEU had 5 tests that they wanted met before agreeing to schools reopening (keeping in mind that schools will open whether they agree or not...) and at the start of July the union position was that most of these tests had been met or partially met.
neu.org.uk/neu-five-tests-government-schools-can-re-open
I'll leave you to read and see whether you think these have been met and to what extent... I'm not sure whether the stance has changed in recent days with cases being on the rise - I've seen nothing official from them recently.
Please don't believe what you read or see in the news about unions preventing opening. They are just trying to keep staff and pupils as safe as possible and have nowhere near the power that Johnson et al would like you to believe anyway.