Matt,
You asked the same question on one of my YT videos so I'd thought I'd answer here (and Mike's already replied as I'm writing this). Hey Mike!
GRE's 310/410 scanners are excellent in receiving the airbands, the best that I've enjoyed compared to my previous radios. I used to use the Diamond HT antenna for the Pro-97, 330T and 396XT (when I had them) and it's a good buy for sure but I've since been using telecoping antennas for both the 310/410 and found them to be superior. I believe that has contributed to the improved reception in these bands. My only other current radio is the 106 and same antenna, same location, the 310 performed notably better, even picking up a local airport's ATIS while the 106 didn't at all.
One of my videos shows the 310 picking up 3 RCAG frequencies from some distance, both aircraft and controller. In regards to milair, I really only monitor it while at the navy base nearby or at an airshow so obviously reception is great but that would be true of most scanners with the stock duckie as I'm sure you know. So I can't say from experience that it's a great milair receiver but I feel it does just as well.
It seems to me you're looking to pick up a new analog scanner, either the 310 or the new BC125AT, am I right? I would love to give the bearcat a spin myself but it would definitely be hard to pick one over the other. That said I'd lean towards the 310 for the added features and minimal bump in price. You probably/may already have a cable for it and software. Does the new BC even have a backlit keypad?
Anyway, those are my thoughts...