I've owned a few diffeent box blades over the ages. Some with fixed rear blades, some with swinging rear blades. Long story short, I own two box blades now, BOTH with hinged blades. And I wouldn't own one WITHOUT. (Woods HB72 and HB84) I have access to a couple Gannon boxes at work, both with hydraulic scarfiers. Highly over-rated unless you're going to be doing a LOT of ripping. (Or your money tree is in full bloom!
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Hydraulic top link is nice. They're probably more useful wth a box blade than any other single implement.
Resting the weight of a box blade on the rear cutter isn't the best way to finishgrade IMHO. A deft hand on the position control is. I do NOT like to use draft control when grading. I want accurate control of the box, and NOT having the draft control constantly adjusting its position.
Just my opinion, and quite possibly worth all yo just paid to hear it