It seems a useful tool to set a starting point for speaker and listening positions, if you can put the speakers where suggested, and if you can sit in the best coloured zone somewhere close to an equilateral triangle with the speakers. However as with many such tools it only fits rectangular or square rooms and although it says it calculates three dimensionally, it is not tailored to the room (I guess it assumes a flat ceiling parallel to the floor, around 2.4-2.7m high. Oddly it appears to measure from the centre of the speaker, whereas in fact what counts is where the drivers are - the front face (baffle) on most speakers for distance from rear wall and centre of the drivers (bass driver in particular) for distance from side walls.
Don’t forget this thread: Speaker placement guide which contains other guidance on speaker positioning (and given the real world differences between rooms, not just their dimensions, all guidance can only be a starting point.
once the starting point has been found, tuning using a tool like REW can then help optimise (some people optimise by ear, but I find REW is a far quicker way, as testing each position takes only a minute of so, and can be compared directly with previous without having to go back and forth a cocuo,e of times to verify.