I have the Leinbach post hole digger. The gearbox and other parts are plenty strong, but the tip is a problem.
My soil is mostly clay with some sand and small gravel in places called iron ore. The factory cutting edge totoally wore off after a couple dozen holes. I welded on some half inch steel with an edge to replace the cutting edge.
When sharp, it digs fine, but the metal wears off in less than a day.
Now I've bought some carbide tips from a Pengo and Lowe bit. I'm combining the two and hope to create a super cutting edge that will last.
If I had to do it over again, I'd pay the extra money and get a bit with the good tip on it!!! Pengo or Lowe seem to be two good choices, but I'm sure there's others.
Also be sure to get a 12 inch auger as the very smallest. You will always have to adjust your holes after you dig them, and the bigger the hole, the less adjusting you'll have to do.
Eddie