Warning: These are the only gauges of strings I have ever owned or tested, so I cannot objectively compare them to any other type. So this opinion applies to alignment tools in general. First, they are very cheap and easy to accidentally break. I broke the case on one of mine trying to put a hose in it. This isn't a problem I usually complain about as most people probably know to be careful with something like string levels. And their intended use seldom exposes them to physical danger. However, because of the cheap housing, they are dangerous as a leveling tool. "Bubble Tube" does not always fit perfectly into the plastic case (in the lower part). They aren't glued or snapped in place and can pop out very easily (popping out isn't exact because they don't even "pop out"). If one side of the tube comes out, it's imperceptible, which will relatively lower your level. Any slight movement of the tube within the housing will cause them to be ejected. This can result in misalignment or waste a lot of time trying to figure out what doesn't match. Their inaccuracy can be tested by placing them all next to each other on a known flat surface and checking for differences between them. Frame. For example, make the top (wrong) part of the body smaller than the bottom (right) part of the body. This puts constant downward pressure on the tubes from the body, keeping them properly seated and aligned.