I am restoring a 1960's Clausing lathe and really need a way to determine level with high accuracy. I saw them, was very interested and finally decided to take the plunge. Pros: It seems very accurate and repeatable. I had to calibrate but I couldn't find anything wrong with it. Just make sure you have a very smooth and flat surface with no movement. Also be patient. After each adjustment, wait about ten seconds for the level to stabilize. It is by no means instant. Actually it's pretty slow. I'm sure they heavily filter the sensor results to ensure stability. I found this to be within the 0.0002 in/ft spec. Bad: This is not a professional product. The base is made of aluminium, it is cast and not machined in any way. to actually apply the blue layer a little thicker to see the contact points. There are three of them! The base must be cast iron and precision ground. Since I'm working with cleaned surfaces these contact points are up and down and don't sit securely on the bearing surfaces. And it's short so any error will be magnified. I'll probably try to finish sand it to make sure the flats are actually flat. about nothing The Ugly: Fees for the app. When you purchase a device, you will receive a "redeem" code. You cannot install it on another phone without paying for the app. What a grab for money. Next year I'll probably have to upgrade my phone and spend money on an app. Why? This is a $400 product. The app is useless without a $400 item! Topping up an app can bring in a small amount of money, but at the cost of annoying every customer. If they want to charge for the enhanced app, no problem, but the app must be free to use the product!