Thanks to all who responded to my question about experiences with the Jang seeder! You guys rock. Compilation below:

Jang took me a couple years and I almost gave up on it, but as information on sizing seed and choosing rollers grew and got passed around the last few years, grew to feel much more comfortable with it.  Last year we did real well direct seeding most of our small ds crops and have experimented direct seeding some that we usually transplant. We also bought the large-seed push model and are working on beans, peas, corn…

We direct market and don’t mind a little less uniformity, so when in doubt will move a size up (i.e. using Y roller instead of YYJ).  Take carrots.  We might spend a little more seed but have more confidence in getting a good stand when conditions are not just right.  Which they usually are not.  And sizing up one roller or going to a 24 count roller doesn’t overseed to the extent that you need to thin - we haven’t thinned since we started Janging.  In most cases we leave the sprockets set to the closest spacing. Again, unless there are perfect seedbed conditions, the thing still skips on us at times, and the 2.5 spacing often fits the bill anyway.

We were happy enough with it by the end of last fall that we invested in a tractor mounted rig and ganged up several units that flex independently (I’m forgetting the model number).  We haven’t dialed this in yet - had a pretty rough season with in fact. But I’m somewhat relieved to hear that pelleted seed may be to blame for some of our failures.  Ganging them up on a toolbar can work, but you need a good, flat bed top with an even surface.  If you’re willing to spend or to make one yourself, Sutton Ag makes a nice seeder sled that can include a roller firm things up in front of the seeders to save you a pass making a seed bed.  

I have a 5 row. I use it for spinach, cilantro, dill, carrots, parsnips, beets, and brassicas. I've found that the impeller plates need to be removed for everything but the brassicas, the brushes do the work but need replacement almost yearly. I like it better than the planet Jr., mini sutton, jd 33 and of course earthways that I've used in the past. 
I would recommend the Local Roots Farm 2011 blog post about the seeder, including the comments (there are a ton of them) in which people discuss which rollers they use for what and bring to light a math error in the spacing chart.  It also points out that some folks are having their own custom rollers drilled to get higher seed ratios.

My conclusions about the JP-1.  

1)  While there are a lot of variables you can manipulate to get ideal seeding rates, I find that changing the set up (gears, rollers, etc)  in the field is awkward.  There are small pieces it would be easy to lose and I need my reading glasses to see the embossed codes on the rollers (I probably need to make some color codes).  I prefer to do all the set up in the barn and only switch between varieties of a single crop in the field.   When I first got the Jang I did a lots of trials tweaking things a little, and usually didn’t see differences as long as I used an appropriate roller.  

2)  We don’t have a perfectly smooth rock-free seedbed.  As a result, we don’t get precision seeding.  We get gaps and clumps.  We have concluded that we are better off with some deliberate overseeding. The double shoe does not work well in rocky soil, takes too much oomph to push it through.  So we go back and forth a couple of times if we need higher seeding rates.  You could also achieve this with the special order 48 hole rollers but we have spent enough money on rollers already.  

3)  We prefer to not use the felt covered spring so we can actually see the seed in the roller as it’s being used.  We have heard the same from others and in the blog comments.  With pelleted seed it’s really easy to see if the seed is actually doing what it’s supposed to do and if it’s getting covered adequately.  

4)  We had a problem with the depth adjustment where we could not tighten the bolt that holds the shaft that determines the furrow depth.  Our machinist neighbor said it was not user error and machined us a new part that had a thicker diameter and was made of tougher metal.  When I contacted Johnny’s, they were eager to replace our Jang immediately at no cost to us but we decided we were better off keeping our machine with the part that had been fabricated.   One of the blog posters talks about modifying the shaft to allow for deeper seeding.   This is disappointing for such an expensive machine.
Hi - We really like ours. Identifying the best wheels/discs and setting to use took some work but it was well worth the money. We weigh out the seed with a gram scale and kept notes of how much of what we planted and which gear and seed discs worked the best for reference in subsequent plantings and years. 

Mimi Arnstein