It is nice to have additional options when selecting what tools to buy and use. I, therefore, applaud your inventiveness and attempt to bring this tool to market.
While I wish you well, you must know that a conventional level that has a cross-vial (plumb level) can do the same thing. If a horizontal element is found to be level and an adjoining element is found to be plumb - then they meet at 90 degrees. The use of geometry, using a tape measure with 3-4-5 right triangles - and/or measuring opposite diagonals for equality are also common alternatives to determine “squareness” . Finally, many of us use quality combination squares or builder’s squares that include level vials. With all this said, I hope that your product will fill an untapped niche market.