I like the idea of the threads for ease of adjustment but they sure don't last long.  I put some on a 7000 planter we put together a couple of years ago.  I didn't do every row and left some of the old ones on.  After one season the old ones were tighter than the new ones.  I finallly bought some of the RK products to fix them and they were great.  I have sold that planter but the 1770 nt we plant corn with is going to get the RK's next year, I am going to make it through one more year with the screws.  \

As for the new planters compared to the replacement parts, I think the quality on new equipment is better than the replacements.  New always seems to last longer than the replacements.