I have both the 20g and 18g (well it is sold as 18g but says 17g on the basket so not sure which is is). I have used both, but mostly the 18g one mainly as it suffers less from channelling from some reason.
From what I understand the baskets are designed to give you the correct clearance to the showerscreen for the given dose of the basket and that you can go +/-1g safely. I would still use scales to make sure you get consistency, though I find for most beans that I get the same amount by weighing 18g that I would by filling and levelling. However if you use high density beans you would get rather more weight by levelling, but then I find that I updose those beans a bit anyway about 1g. I reckon you would be OK with just fill distribute and level, but don't be lazy, get some scales!
I believe you are correct about the VST to LM comparison, the LM ones do not go through as thorough a check.
I can say that I get far better consistency than with previous baskets I have used, particularly when running restricted shots, no more slow drip then gush at the end.