One feature that I do not like about these types of calculators - inputting my financial information on a web page - who knows what happens to that. I am not suggesting that it is emailed all over, but it could be placed on your harddrive in a form where other sites can look at it.
It also provides the providers of the web page information about the people reading the page that may be considered private. For example, by all of us running to see if we can RE and inputting all our financial information, all this data can be collected for the webmasters to conclude "we could charge XXX for this service, most of our users are worth $ 250,000 or more." - get the idea. If people / businesses know you are able to afford a service, they will try to charge you.
I think that by people placing all this info on these calculators will bite us big time some day.
For example - seniors get discounts for movies, dinners, etc.. and a LOT of seniors need this help. BUT - another side of the equation is that a LOT of seniors are riding on this subsidy even if they can afford full prices. I tell my mother, when I get to be 65 – the merchants will ADD a senior fee to my purchase. All this will be because our financial info is slowly being collected.