Shiva Unreal is also just Shiva Extreme, but tuned for level 80 characters. If we were to compare her to ShB's current Extreme Trials, she would be the easiest of them all (as she was the easiest Extreme Trial in ARR days, like Garuda EX). The only hard part about her is Glass Dance and Avalanche.

As for how Raid Finder works, it's for when you decide to do the fights via the DF instead of the PF. Having Duty Complete checked means you will only encounter people who have cleared the fight as well and you can only have Duty Complete checked if you have completed the fight itself. Otherwise you can only choose Duty Incomplete, which means you will only encounter people who haven't completed the fight... but then that's when the other checks come in (basically, having specific things checked = who you will party with in DF).