Just got this reply from the team:
"NSE drives are FIPS 140-2 Level 2 validated. FIPS 140-2 Level 2 requires physical security measures (e.g. tamper resistant screws, security chips, etc) as opposed to Level 1 which is software only.
NVE is FIPS 140-2 Level 1 validated.
Does that help?"
I've been told to always recommend Flash Pool with NSE as it's apparently the only available option. Not really a technical explanation and it doesn't help those of us in regions where FIPS doesn't apply.