I would say that the level of understanding required is sub-A-level, but the volume of material is nearer second year degree.
In other words - it's mostly about memorisation, and lots of it.
However, as you've already realised - question spotting is a mugs game. Learn the subject properly, then delve into question banks.
On met specifically - you will never know enough about it, but it's worthwhile trying to. I nearly got caught out by a sea fog today, sonetime this evening I'll get the books out and see what I forgot about how it forms.
G