Using the tool alone is not as accurate as the guestimation of IBU within a recipe where the process volumes, gravity, and losses all have an effect on the IBU of the resultant beer. You must also keep in mind that the calculation of IBU in the final beer is purely a SWAG (Scientific Wild A$$ Guess) as the models really only give results based upon the tested end of boil values for the process the wort was created. It does not take into account the effect of yeast strain and fermentation vigor on the presence of bittering compounds remaining in the finished beer.
While I am not sure why your need for the tool, I highly recommend bench marking your perception of bitterness between your beer and a commercial beer of similar style with a known IBU. That said, there are not many craft breweries who do actual IBU tests but are reliant upon sensory panels for consistent product out the door. So test results from some of the bigger craft names would be the best products to use for comparison. Sierra Nevada Pale Ale is one of the better beers to use as a standard and there are certainly good clone recipes out there to use for side-by-side tastings.