I think the Earvana system is a great choice for the price. I've never used the Feiten system, but I have two guitars with an Earvana nut and on both of them, every note is in perfect or very close to perfect tuning all the way up and down the neck. You need to make sure you're using a strobe tuner to get the best results. It will work for non-standard tunings, but you will have to have the slots widened if you're using strings heavier than 10-46.
Ryan