They are definitely not as invasive or prolific as either neglectum or even latifolium. Seed is produced but it does take a few years to grow to flowering size. I have seen the bulbs on sale in a couple of garden centres over the last few years, so they are coming into commerce. The clump I have would have been planted about 3 or 4 years back and now has about about 10 individuals from a 2 bulb planting.
Now if you could find a clump of one of the 'yellow' ones, that would be special!