As far as the MPH PHAP experience: There used to be two separate programs, PHAP and PHPS. The first was geared towards an internship/bachelor's degree model, and the PHPS was geared more towards master's degree holders with some experience. It was designed as a way to learn public health program planning, implementation, and evaluation. This started prior to the phenomenon of people going straight from bachelor's to their MPH as a starting point, so that program was all geared to expand your knowledge and mentor you into a leadership position.
In 2013, CDC merged the two programs. Dr. Frieden wanted the PHAP classes up to 200 and the easiest way to expand the program was to remove the requirement for experience and move everything under the Pathways recent graduate authority. So, now, PHAP still is the entry level, but now the eligibility has expanded.
There are two big problems with this: First, the program is geared towards trying to convince people who were thinking of med school or something else that Public Health is a great field and they should pursue that instead. That's a perfectly legitimate goal - but I just dropped 40 grand on a master's degree, I KNOW already what I want to do.
The other problem is that much of the programming, online training, webinars, etc. is geared towards someone who is coming out of a bachelor's degree with no real-world work experience at a professional level. Things like how to politely send emails, how to dress for an office, how to interact with your supervisor, how to listen - lessons that I already learned. Don't get me wrong, these are very valuable lessons, but I am 35 years old and came into public health very late and much of it, when it's not wasting my time, is talking down to me (as a perception, not necessarily in reality). But I knew this when I came in, too, so I just roll with it.
The real benefit of this program is to get you hands-on experience at a local, front-line level. I have 8 years as a firefighter/EMT, another couple as a life safety inspector, and then 5 as substance abuse educator (with a couple years of killing bed bugs thrown in there). I don't have any public health experience, though, except on the periphery, so the opportunity to get a paycheck (such as it is this first year), add a couple years of good experience and get to put CDC on my resume was a no-brainer, even knowing that I'd be an old man in the program comparatively.
I went to East Carolina for my MPH and knew I wasn't going to be sticking around the area after I got done so I did my internship somewhere where it wasn't going to lead to a job (although one was offered it turns out). I didn't think I was going to have the science chops or connections to land a job quickly, and if I did, I'd be jumping in at a bottom rung somewhere and would be taking it just to get a job. Actually, that happened, I took a contract position in Atlanta, left my wife in Greenville, NC, and had moved away for 6 months with no promise of anything past that. So 2 years of work guaranteed with the premier public health agency in the world sounded great. If you have a different experience, better contacts, more promising job options in a field and region you would be happy for, then this program may not be a good idea.
The big thing is this: remember that this program is, just like a master's degree or anything else in life, WHAT YOU MAKE OF IT. I ended up getting assigned to Quality Improvement my first year and hate it, and didn't want to do that and don't think it's actually public health - but you know what? It is certainly helping me learn how to run a health department, and I'm pretty good at it and have become a valuable resource to my colleagues. I also am in Chronic Disease (they screwed up the host site application)...I went and got my MPH to do infectious diseases, particularly nasty arboviruses, and have zero interest in that part of the field, but it's helped me learn program planning and delivery. More to the point though is that I've advocated for as much training as I can get my grubby hands on to keep my skills up and expand my marketability, and I've deliberately volunteered for any assignment I can get my hands on (particularly when it's in our Disease Control, Prevention, and Preparedness department).
Heck, last week I spent all week getting a national certification as a Child Passenger Safety Technician and learning about car seats. Do I care much? No, but by golly that will look good on a resume, will help you help your community, and will further round you out as a candidate for later opportunities.
PHAPs are there to expand the capacity of local and state health departments, and to me, that means picking up the slack wherever I see it. If you show up, learn quickly, show your worth, and appear hungry most host sites will feed you what you want, give you what you need. Go in demurely but confident and make these two years YOURS, whether you're fresh out of your bachelor's or you're coming into this with experience. This program will be as good as you make it.
! I didn't get a call until September (yes a month before the program started)! Also if anyone wants any insight into the program and the onboarding process feel free to message me. 
