Personally I don't think that there is really anything that special about the Crown MkII.
But in all seriousness, I have them in .177 up to .25 cal at the moment, and have owned a .30 in the past. The MkII Crown makes me look like a better shooter than I truly am. And the GRS stock just adds to everything I like about the Crown.
I have had long barrelled Impacts, and while their tuning can be easier (don't have to remove action from the stock to fine tune hammer spring pre-load), I just can't shoot them as well. For me a traditionally wood stocked rifle off the bench works the best. And the GRS stock, once again for me, is the optimal configuration. I never bought into the custom stock trend when shooting firearms. I guess that I did not know what I was missing. With the GRS stock configuration and its easy adjustability, I immediately felt comfortable over it, and noticed that it made the gun much more stable for me on the bench. The 'long range' in my back yard is 61 yards, and I can consistently (and without too much trouble - kind of casually) achieve 1/3" 5-shot groups in favorable conditions (no wind). That's with .22 and .25 - I'm not quite there yet with my .177 Crown.
The guns in the photo above are not too old, but I have not had any issue with any of them, and they do get shot regularly. And most times I can find a combination of hammer spring wheel set-point and transfer port wheel set-point which gives me the muzzle velocities I want to begin accuracy testing, without needing to deal with hammer spring pre-load fine tuning.
And I absolutely love the Crown w/380mm barrel configuration. That configuration always seems more accurate to me than it should be. So handy too. And a Crown with 380mm barrel has hooked more than a few new airgun shooters up at my Cowboy Action Shooting range.
Does FX have a GRS Continuum kit available? If I was going to get one Crown that is what it would be.
NOTE: If you have smaller sized hands (I wear 2XL gloves) you should handle, or preferably shoot, a GRS stocked Crown before buying. Even with the ability to adjust the trigger back in its housing on the Crown, it can be a long reach to it for some.