Yeah, th 504 is not cheap if you were originally dropping $280
I've never used the Sachtler Ace but have used much more expensive Sacthelrs and they are very nice, so I imagine the build quality would still be very high. The 504 is also quite good, so again I'm sure the 502 isn't that much of a step down. It all really depends on your budget. If you can afford to go for the more expensive tripod, then it's going to be a better tripod; if you can't quite afford the extra $215, you're not going to get a necessarily bad
tripod. It just won't be as good as a more expensive one (as is to be expected).