Greetings all.
I (barely) passed my NRPP exam today with knowledge exclusively based on InterNACHI’s Advanced Radon Measurement Service Provider Course. The exam was way harder than expected. I may not have put enough time into it if not for the warnings above, so heed their advice. I squeaked by with 73% but got it done first try. If it was not so expensive, I’d study again and re-take to feel better about my score. 2/4 on ethics! Wow.
Many questions seemed to have multiple right answers. Example, which device is more susceptible to air movement: AT, LS, EL, GS, … - I thought they were all affected by moving air like in ventilation, no? The questions are also thoughtful. 100 questions, 2 hours which was plenty. The less you know the more time you’ll have 
Formulas and calculator are provided. Very little math. Know how to figure which is more exposure: 52 years in 4 pCi/L at 0.4 ER versus 7 years at 30 pCi/L at 0.6 ER, etc.
I agree with all comments above that the NACHI course is not an ideal basis for NRPP exam, however its all in there including the long boring parts.
My tips:
(1) Download the Advanced Radon study guide - there is a link to it near the top of the course. It is easier to re-read in PDF format than to step through the course page-by-page again.
(2) Many questions are based on the EPA Radon guides. Those are in the NACHI course, or get them at https://www.epa.gov/radon/publications-about-radon.
(3) There were more questions about mitigation than I expected. I skimped on those since that’s not what I’ll be doing. Mistake.
(4) Know all the device types, not just the one you use/plan to use.
Point is, you really have to cover all elements of the course.
Good luck.
