I bought one about 2 months ago and am also very happy with it, thanks for the pictures of the insides. I've done a lot of tig on thin wall steel tubing so far. I also tried out the arc welding with 6010 and 7018. I found it comparable to my old Lincoln tombstone, it amazes me how that much power can be in such a little package. On the tig side, I think the arc start is a bit harsh, I would think they could turn down the amperage on that a little with no ill effects. When I have to weld on something thin, I start on a thicker piece of scrap right next to my work, then slide over to start welding. The other thing I don't care for is the 15 second post flow. That uses a lot of gas when I'm tacking, or welding at low amperage on thin material. Maybe it's necessary to cool the torch or tungsten or something, not sure why they did that. I think the controls are really nice, I've used the pulse quite a bit already. It would be nice to be able to change the % on the pulse, but for the money I'm just glad it has the feature. I also really would have liked 2T/4T because I'm often laying down or in some crazy location where it's hard to work the foot pedal. I switched to a gas lens because the original cup on mine wasn't concentric around the tungsten and I felt there was more contamination and popping in the weld than there should be. The gas lens completely cured that, so my suspicions were correct. I think they didn't get the threads machined true on either the cup or the collet holder.
This machine was a tough choice for me because for the same money there are several imports that really have many more features and more power. In the end I decided to go with something that is supported locally and has a good warranty even if I have to sacrifice some features. I also got a very good deal from the local Airgas store, I'm a welding student at the local community college so they threw in a free bottle of gas with the purchase.
Lincoln Square Wave 200
Lincoln 225 AC/DC
Harris Oxy/Acetylene torch