No. I just pointed out that a NERVA is basically a smallish nuclear reactor with only a partial shield and limited redundancy, with relatively temperamental reactions as any device that flash-vapourizes cryogenic propellants (rocketry is full of spectacular failures), whose main (and only) cooling is propellant and lacks an internal coolant pool like land-based reactors that even if "standing still" is going at more than 7.6 km/s as anything else in orbit.

Saying it is safe as a land-based powerplant with a full half-meter metal shield (and concrete) plus at least triple-redundant cooling systems plus a safe-ish containment vessel of concrete ready to catch it if it melts down, plus enough coolant in it that it can be left without any cooling for a couple days before it starts having issues is frankly wrong.
On a tangent, all this safety has a price, Three mile Island wasn't a major accident, but ended up costing a lot as both lost revenue and clean-up costs.
It's these ridicolous costs that are killing uranium-based nuclear designs, as they simply make no more economic sense after the need for plutonium (for nukes) dropped dramatically. The future of nuclear is either with Thorium or back to lab-only breeder reactors.

Back to topic, there is "safe nuclear" and "less safe" nuclear. NERVA is less safe. It's the difference between a mono-cycle and a tricycle.
It's remarkably safer than that concept they had of atomic-powered bomber (with a smallish nuclear reactor onboard), and the other thing called Project Pluto, a nuclear-powered airbreathing missile, but does share some of the drawbacks.

Radiation generated by it is harmful for other spacecraft (as it is neutron radiation, while cosmic and space radiation in general is mainly charged particles and a shield that stops one does not stop the other), if it goes rogue or whatever it can destroy satellites or kill crews of other vehicles/stations by just passing at less than a few km from them (think of how dangerous docking maneuvers become). And again if it falls down, you better hope it ends somewhere in the Pacific or you will have to create a big exclusion zone.
It also makes a pain any repair in the general area.

Efficiency is basically down to how much power the engine can generate. In their case it hits a upper limit as the highest tempt the care can go without melting, while the best models that were still on paper (particle-bed kinds) using the best fuel (hydrogen) can provide around 9 km/s of delta-v (vs the 8 km/s of the real ones), the theoretical upper limit is 12 km/s. To do better you have to design liquid-core and gas-core nuclear thermal rockets, that are even more temperamental and dangerous.
That delta-v is easily in the range of conventional chemical rockets, if you make two stages, and the total vehicle mass would be around the same since NERVA's are pretty heavy and you cannot really sidestep that so easily.
So yeah, you use less propellant, but not a lot less, and you add risks you would not have, and costs and complexity.

Imho, they were a dead end. Cool but not practical. Project Orion (pulsed nuclear propulsion) on the other side, it was much more interesting, if a bit sketchy in its ability to survive its own propulsion system.
The same question remains for most engine designs with enough power to go anywhere in less than years.

Btw, have a look at [link]
it's Atomic Rockets, a great site to learn the ropes of well, rocketry.

Yes, I have. This comes only a year after Planetary Resources made their announcement about doing the same. That's 2 companies now with long-term plans on mining NEOs. Along with companies like SpaceX, Reaction Engines Limited, and Bigelow Aerospace, we might have an interesting future to look forward to in the coming decades. I hope to be a part of that future.