Estibot is a great tool for getting data on a bunch of domains at once. Admittedly the actual estimated domain value is fairly useless with brandables. Most brandables are completely subjective and are beyond the scope of any automated appraisal system, not just Estibot.
That being said .. if it pumps out a bigger number it'll get me to look into the domain a little more to see if I didn't overlook something. The reverse is true as well, if it gives a really low number when I thought it would be high, then it'll get me to double check if I didn't read too much into the domain .. or sometimes a surprisingly low number is quite simply an indication that there's a typo in the domain .. lol.
I track about 200 domains going to auction per day (but only buy a very very small amount of those). It's a quick way to pull out CPC, search volume and number of searched pages. These certainly are not the only factors involved when I evaluate up to what price to pay for a domain, but they certainly do help.
When it comes to pure brandables your gut feeling based on general knowledge of the industry in question still ends up being the biggest factor.
At the end of the day it's a good tool that helps you get some data to help you decide your own personal evaluation of a domain.