I bought a Jang JP-1 last year and have found it a great improvement over my Earthway, worth the price difference. The Jang is much heavier making easier to keep in the ground, though with my clay soil I really wish it were twice a heavy. The JP-1 is better with small seed crops but it does work for large seeds like sweet corn, but expect some misses and doubles.

The Jang uses rollers instead of plates, with the roller selection based on seed size. Depending on the seed size sweet corn will require roller size A, AA or N, at least the seven varieties I've planted with it. Spacing is set by the choice of front and rear gears used, six come with the unit. Everything, but planting depth which requires a wrench, can be adjusted with fingers in the field, no tools needed. There is even a copy of the spacing guide attached to the inside of the chain shield.

My only real complaint has been the planting shoe. Its used to set the planting depth and attaches to a steel rod held in place with a set bolt. The rod will bend back if you hit a stone or patch of hard clay. I've cut a selection of wood blocks to set between frame and back end of the shoe. The block height used varies with the planting depth.

I plant half an acre of sweet corn each year. Doing that with the Earthway was a struggle but the JP-1 has really made job easier. I'm serious considering (i.e. saving my lunch money) to buy a Jang TDR for next year. The TDR is designed for larger seed like corn and pumpkins and should handle them more preciously then the JP-1. The downside is the TDR is $650 compared to $380 for the JP-1.