Is it worth it, for me yes it was! I have an 8' heavy model with the pair of same angled blades and do not own a back blade nor a box blade, both of which I have used over the years and they all three have their own purpose. My needs were mostly to have a blade that worked a lot of road easily. With the land plane I just drop it down and head out staying to the right edge of the road, half mile later turn around and go back hanging to the right edge. Since it slides along on the skids I don't have to work at controlling the cut and the angle of the blades moves gravel back towards the crown as the rocks build up and fall over the top of the actual blade. A couple of passes each way usually gets things in pretty good order.
The one I have was built by a company here in MS, if I were to build one there are a couple of things I would change. First I would want it longer front to back to span the waves that can develop in a road/driveway with more distance between the two blades and the blades would be set at a bit sharper angle to give more slice to the cut which would also enhance the crowning effect. The more vegetation your road has the taller the sides need to be so there is clearance between the top of the blades and the framework that the 3 PH hooks to. Have had to stop lift and clear mine a few times due to the amount of grass that can grow up in our roadbeds over the summer. Another feature would be adjustable depth of cut either by numerous bolt holes or preferably by a type of screw jack method with a clamp mechanism on the ends at the side plates.
Now, if you really just want to level with no crown then a modified short 3 ph version of they Rayne Plane would be the ticket. Build the side plates 8' apart at least 10' long, and put 3 7' blades in an alternating angled pattern with a spreader rake at the backend after the 3rd blade. Front blade would be flush to the right side and end short of the left side the 2nd blade would be flush to the left side ending short of the right and the 3rd blade would set like the first one. This would slice and move your material back and forth across the road giving the best chance at filling and leveling the low spots with the rake spreading the windrow after the third blade leaving a bit of a crown. There are times I have need for just such a blade and have thought many times about building one using an old mobile home frame. Might even make it tongue pull rather than 3 ph with a hydraulic drop down axle just behind the mid point.