I've owned the push-pull version, the two-ring version, and now the 70-200 - so I can speak from a bit of experience.
The push-pull version is just as sharp as the two-ring version or the 70-200. I never had any CA problems with my lens, although that could be due to sample variation...I'm not sure. I've used the push-pull version with a D70 and a D200 with equal success. So, if you can score one cheaply, it's a good buy.
HOWEVER...the push-pull version is a bit slower to focus. That fact alone might be enough to scare someone off from a purchase. This really comes into play when shooting sports or other fast-action shooting. Also, the lack of a tripod mount is inconvenient. I've seen gizmos that suposedly compensated for this missing element, but have never personally tried any of them. I'm sure they have their value, but I can't attest to their exact usefulness.
The push-pull version can be mounted and carried on a D70 with no concerns for the harm to the camera's mounting plate. I've carried this lens (mounted to the D70) for 14 consecutive hours while shooting an outdoor music festival - and had no problems...other than a sore neck.
So, basically, if you're not going to shoot sports or birds in flight...or you don't need a tripod...the lens can be a great value.