I'll contend that Bru'n Water has provided thousands of brewers with the ability to quickly refine their brewing water adjustments and enhance their beers.
It's not an either/or thing (see below). I used to believe that the average brewer could benefit from the intricacies of brewing water chemistry at the same time he could be protected from them hiding them in a spreadsheet which would present the users only with the 'coarser' results knowledge needed to practically manage brewing water. Accordingly I prepared a spread sheet for my local club members which does what the popular ones do and all manner of other things as well. But I found that isn't really the answer as putting a powerful tool in the hands of those who don't really understand the underpinnings is conveying enough knowledge to be dangerous (not that ruining a batch or two of beer is really dangerous but there are analogies in other fields of engineering that are).
Measurement is certainty, but the untrained brewer is still left not knowing what to do with that information.
It's quite clear what he should do. If mash pH is too low, don't use so much acid next time. If mash pH is too high, use more acid.
Information without the knowledge on how to use it is: Useless.
As noted, what is to be done is very simple if one knows the actual pH and a brewer with a meter does. The spreadsheet user is shown an estimated pH based on an imperfect model and questionable data. The uncertainties are much greater. If the true pH is 5.55 the meter user will read something close to that (if he calibrates his meter properly) and conclude that he should either accept that or add acid. If a spreadsheet or calculator informs him that his mash pH is 5.3 he may decide that's too low and add base doing exactly the opposite of what he should do. Incorrect information is worse than useless. If the spreadsheet or calculator shows the mash pH is 5.7 he may decide to add more acid than he should. In either case he has been ill served by the calculator or spreadsheet - something easily avoided with a meter.
But the spreadsheets aren't usually that far off some say. Often they aren't. But sometimes they are. How do you know when they are? By taking a pH measurement.
A tool like Bru'n Water further enables the brewer to make appropriate decisions for adjusting their brewing water.
Where something like Bru'n Water is useful would be in a case where the brewer, for example,
measures a pH that is too high and then turns to one of the spreadsheets to see what sort of things one can do to lower pH. Even if the actual pH is 5.55 while the spreadsheet estimated 5.3 he can see that adding lactic acid lowers it and conclude, rightly, that adding some lactic acid to his mash is the thing to do. This is what I was referring to when I said above that it is not an 'either or' thing. The prudent guy will take valuable input from wherever he can get it.
Its the craftbrewer and homebrewer that brew something different every week that don't have the opportunity to brew and rebrew a recipe a half-dozen times that need a tool like Bru'n Water.
The tool they need is a pH meter and many of them have become aware of this. As noted earlier a good spreadsheet is great for helping them determine what to do based on the pH meter readings they get.
They need a tool that gets them in the ball park every time. Trial and error is more effective and surer than any other method,
Certainly trial and error is very inefficient compared to a program that does a brew and then does some analysis on it. You can get from good beer to very good beer in a couple of steps if you don't work in the blind. There may be more to this than just pH meter readings of course but knowing process pH at various points is an easy to implement and powerful part of developing a beer. This is not to say that once one knows how to hit mash pH of 5.42 and kettle pH of 5.10 he is finished with development. Fine tweaking will take one from very good beer to excellent beer.
I still stand by my original statement.
I think there is room for more than one opinion here but there are few investments in brewing gear that top a pH meter in terms of shortening the path to very good beer. A tyro with a flashlight has got to be better able to find his way through the murk than an expert in the dark.