i'm warrantying my 2018 440i, i paid £359 for the bmw insured warranty with £250 excess for the year
your 330i should be similarly priced, except if you don't already have the bmw insured warranty in which case the first year will be more expensive (+25%?)
as with any warranty products, it's a waste of money if you never use it...
but if you needed to claim on the warranty and did not have it...you'd wish you had it
do i think it's worth it? yes, solely for the peace of mind if anything major goes wrong i'd just shell out £250 instead of £xxxx