I think the biggest factor as to whether or not this is a good deal would be how you use your phone. I know a family therapist who is on-call for her clients should they ever need to talk to her, and the free incoming plan works great for her, although when she calls people she tends to tell them to call her right back.
As far as I know, I haven't heard of any hidden charges regarding incoming calls. However, if you are on an outbound call and use call waiting to take an incoming call, you will be paying for the minutes that call #1 is on hold, same thing if you place a 3-way call and the first person on the line was an outbound call, you are paying for their minutes.
This is ok as long as you have enough outgoing minutes included in the plan, but keep in mind if you go over your outgoing minutes, the per-minute rate is 45c/min. As with any Sprint plan, I think it's definitely worth $10 extra for nights & weekends to start at 6pm instead of 9; you don't have to pay for as many minutes in your plan that way.
I think this is better than Fair & Flexible if it suits your needs, and that's something you'll have to decide after you consider how many incoming vs outgoing calls you make, and do you think it will bother you to always call people and tell them to call you right back.
