People like them because they are fast, accurate, can be calibrated, and come in pretty colors! That said, they are also expensive and as much as I appreciate them, I haven't coughed up the money for one.
By "consistent temperature" you mean having the mash all at the same temperature? I think this is a safe bet if you have stirred things up. You'll get cooling at the margins obviously as time progresses (especially if your mash tun isn't insulated) but the temperature after stirring should be quite representative for the entire mash volume. As the edges cool it will draw heat from the middle and keep things fairly distributed. What steps would you take if you found that the temperature near the bottom of your mash tun is 1/2 degree different than the temperature at the top?