We had the BluJet seal-pro (actually, an earlier version, but same idea) for many yrs on a DMI bar. Those sealers were the best thing since sliced bread. Worked great for us. Now they offer spring assist, which might be helpful for fall work. But, for in-season sidedress, we did not crave any extra push. They were built plenty heavy. Never had a bearing go out either. Make all the adjustments you need w/a 3/4" wrench.

This is ours a few yrs ago:

http://www.youtube.com/watch?v=Oy9InzF8tiQ