Can't comment on the plastic mounting rails, but I have looked at and played with the drive mounting grommets -- in the ARM Systems Stealth PC review
. Here's how I would rank HDD decoupling effectiveness:
1) Elastic suspension (DIY)
3) foam bed (DIY - also depends on foam softness)
4) EAR grommets
5) rubber grommets / Smart Drive -- although Smart drive might be closer to the EAR grommets
Anyway, that's just my opinion. I've played around with all of these & you know I have reviewed them, but not always A/B, so I would not consider the above totally verified, and there will be some variance depending on your particular setup anyway. Still, I think there's little question about the first 3. The NV-III matches the DIY suspension if the bottom pads are removed so the drive is really allowed to "float".