I bought the Oregon Professional 620 bench grinder a few years ago. Granted, it was over $400 at the time. Not sure what it is now.
I only have the one saw, Stihl MS391. I have several chains for it. I abuse the crap out of my saw. I got tired of digging out stumps with my backhoe, and on many occasions, simply dug down and cut the stumps off several inches below the surface. I might get through a stump on one chain depending the size.
I sharpened my chains by hand for years. Got quite good at it, but it takes time and skill. Buying this grinder has defiantly changed the way I sharpen a chainsaw. For a while, when I needed to sharpen the chain, I'd simply remove it from the bar and add a new one. The old, dull one would go into a coffee can on the bench. After I collected a few chains in the can, I'd sit down with my grinder and sharpen them up. Now, having a collection of sharp chains hanging from a hook in the shop, when the saw gets dull, I just swap out chains.
I have also made it a money maker of sorts. My neighbor has a side business cutting firewood. He goes through chains. Before I got my grinder, he would collect up his dull chains, same as me, and take them into the local hardware store to be sharpened. They charged between $6-10 per chain depending on length. Since I got my grinder, and since I live so close, and since I'm good at it, he swings by my shop every once in a while with a case of beer and a bucket of chains. I spend a few hours BSing and grinding. When I'm done, he hands me a wad of cash and I hand him a bucket with sharp chains. He saves money, and I make a little. But more importantly, I'm a value to my neighbor and others for this service.
I love my grinder.