The most obvious and severe flaw, is the steel backing plate on the stone. It rusts. That’s right. It rusts. Even if you don't use it often, the stone doesn't dry out for weeks. And to compound the problem, Makita chose to use a very brittle adhesive to mount the stone to the backing plate. Because the two unlike materials are held together with a non-flexible bond, the adhesive develops fractures which allow water to seep through to the steel. Steel expands up to twelve times in volume, when it oxidizes. This expansion lifts the stone from the wheel, resulting in a wobble that increases over time. Eventually the stone becomes unusable. Makita should consider a one part polyurethane adhesive, such as that used in the marine and automobile industry. When the stone failed on my first 9820-2, I pried it off of the backing plate and remounted it in a bed of polyurethane caulk. I had no more trouble with that aspect. The spindle/flange assembly which is driven internally and the stone is mounted to externally is steel as well, and corrodes to the point where the threads disintegrate. I fixed this by re-tapping the hole, but threw away the knob because the threads didn’t match. This was no great loss because the threads were rusted off as well. Amazing! No more quick mount. Have a wrench and an assortment of washers on hand to mount the stone. There is in fact, not a single piece of stainless steel used anywhere on the Makita 9820-2. Why doesn't Makita use stainless steel on something that's intended to be wet? I am amazed and perplexed by this lack of common sense in design, every time I walk by an armada of stainless BBQ grills or stainless appliances at my local Home Depot. In addition I purchased the expensive 6000 grit stone, which had a wobble so bad, I couldn’t see the edge of my carving tools. This is a polishing phase. You don’t need to look for the ”wire edge” and so I performed this step by feel. I stopped using it all together, when the up and down wobble became impossible to work with. I now use an 8000 grit bench stone to perform this task. I am in the fourth year of using my second sharpener now, and again experiencing all of the above problems. Makita's earlier models had an issue with the nylon gears not meshing properly, due to the plastic housing impeding moving the motor in its slotted brackets close enough for proper engagement. My first sharpener was just such a model and has afforded me with much knowledge, but my relationship with Makita is souring. Why did I buy another? It offers a large flat grinding surface, which is invaluable for honing and polishing the backs of chisels and plane blades. It is gear driven as opposed to belt drive, and believe me when you start to hone the back of a plane blade and it starts to “drag”, you’ll really appreciate that. I can only attribute the positive reviews it has received, to the duration of use. I’ve been using my current unit four years now. If you have any doubts, call Makita’s toll free number and speak with tech support. One star for the status quo. It's sad, because it could so easily rate a five.