It's very solo-friendly and casual-friendly aswell. Most things can be done solo and as was mentioned, there is a duty finder for battles that require parties so you don't have to sit somewhere shouting for parties. Experience is almost mindlessly simple to achieve when you know what you are doing and you will sometimes find yourself not wanting to play because the levelling is soo fast that you will want to take a break to slow down
So if you only have an hour or two to game, you can still log in and get a quiick level on a job with leves or fates and hop off when you want
Really, the only time you don't want to use duty finder is for the end-game content for wins. Duty finder is great for say getting practice in the Titan hd fight but don't expect a win. It
can happen, but don't count on it. I personally went through the entire story mode with DF parties and I can say that I'm a better player because of it