I've done the non-private RIP
HHN tours 2 times now and already paid for it this year.
Basically the tour allows you to follow your guide to the front of the line at all the houses, often taking a different path to get to the front of the line. That gets you in without a wait. I've done HHN with an express pass and the RIP tour is much better but is also twice the cost, even with the annual pass holder discount. Note: Everyone in your party can get the AP discount, even if you are the only one with the AP. That applies to the HHN tickets too. My wife and I are going with another couple and they saved about $100 on their HHN ticket and RIP tour as I'm an AP holder.
The tour lasts about 5 hours but it depends on how fast your group moves, how long they take at potty breaks, and which time slot you pick. (There are 7pm, 7:30pm and 8pm)
The time slot is important as during your tour, you will have VIP seating at the Halloween show (Bill and Ted) as I recall. Depending on which tour you get, you may have to wait slightly longer for the show to start. Also, if you do a later tour, you will have less time on the rides before the park closes.
After your RIP tour, your tour tag acts as an unlimited express pass on the rides that are open at Universal Studios. It does not permit you to use the express pass lines at the houses. Note: It is an unlimited express pass, unlike the regular express passes being sold that night, meaning you can use it more than once at each ride.