The Keck asteroid retrieval concept looks rather professional
Here was an interesting piece from a JPL worker. He and I disagree on a lot, but he is spot on here:
It's an inescapable reality that getting to and from that asteroid will take a large spacecraft.
I look at this new company animation, and it doesn't add up. Those tiny spacecraft simply can not contain the energy to get to and from those targets via chemical prop. Are they ion engined....then where's the power to drive it, those solar arrays are far too small. They lack high gain antennae, so from 10's / 100's of millions of miles away, how are we communicating with them. Where's their spectrometers to characterize the objects of interest.
Could you do a smaller mission than OSIRIS-REX. Yes. But certainly not as small as this company claim. And smaller means less capable. We would not learn as much about the asteroid as we will with OSIRIS-REX.
Start with a payload....work backwards to the spacecraft from there. OSIRIS-REX isn't big just for fun. It's big because it's very capable and will do far far far more than a smaller spacecraft could ever achieve.
Smaller isn't always better.