I think the "needle large" is correctly named Mic. pt. 'Taiwan' - it is considerably larger than the true Mic. pt. 'Needle leaf', and not so dark green.
I have tested them both, and they're notvthat difficult to grow. Not quite as tolerant as Mic. pt. 'Trident' or 'Narrow', though.
The true Mic. pt. 'Needle leaf', by the way, does really not like growing emerse.
- I agree, you will find true Mic. pt. 'Needle leaf' difficult to obtain, and also agree young individuals may be traded incorrectly, because they are hard to tell apart.
IMO Microsorum pteropus in most of its variations will grow quite dense - it is mainly depending on good growing conditions (added CO2 f.ex.).