TLER is IMHO almost irrelevant for consumer level NAS.
What's confusing about consumer NAS, and whether a Red drive should be purchased instead of Green, is how the RAID is implemented. Only RAID implementations that rebuild data from parity on the fly, without dropping the disk out of the array, benefit from TLER. So-called "software RAID" tends to not rebuild data in the case of minor sector errors, and they also are tolerant of non-TLER drives. They'll just wait for the drive's ECC to recover the data, whereas the more sophisticated RAID will accept a sector error from the drive and immediately rebuilt that RAID stripe from parity, all without dropping a drive from the array.
But it's totally non-obvious, I feel, what kind of RAID behaviors we actually have in consumer products. Some of the embedded consumer "hardware" RAIDs are actually using dm or md raid, so it is actually based on software RAID but appears to be hardware RAID - hence the distinction between software and hardware RAID is problematic.
Then the speed seem irrelevant too as on the NAS you will be limited by the network.
Yeah network saturation for GigE is happening with a single disk now. However, rebuilds can benefit from additional performance.
Head parking can be turned off in green drives.
Yeah I don't know if this is really a good idea or not. WDC support told me they've never seen a drive fail because of frequent head parking. Considering the tolerance between head and disk surface, any flaking surface coating is a head collision risk, and vibration and movement of the drive causes very small near contact with the surface that wears the head and platter surface - it may very well be a good idea for head parking to occur frequently - even if the sound and delays unparking it are slightly inconvenient.