Rating and Chess Mentor/Tactics Training

- There is no one "true" rating. There are several, eg., online (correspondence), online 960, live ratings for different kinds (blitz, standard, bullet), tactics trainer &c.
- No, they accrue points to their respective ratings.
- See (1) above.
- No.
I do find value from the ChessMentor, videos &c. Wish I had more time for chess though. Yes, you can discontinue at any time but I don't think you will get a refund for the remaining time if you, for example, have a one year membership and wish to cancel it after a couple of months.