Pros
If you can survive the politics and grind out the mandatory years in each position (minimum 7 years to make it worth your while) with zero fringe benefits (no bonuses, no compensation for expenses, ect...), the rewards are great for area superintendent and above once you start vesting out accounts after 5 years. If you have a ton of kids too, the healthcare is great because it is completely funded by the company.
Cons
It's a straight up pyramid scheme that is not worth it by any measure. They start you out at one of the lowest salaries in the industry as a field engineer. This position is often incredibly disrespected and treated like children, even by office engineers (a "promotion" that you receive zero additional benefit for). If you make it through 5 years of field and office engineering, congratulations you made it to project engineer, which is more or less the project managers punching bag and most overworked position in the company. But hey, at least you got S units now, right? You've been working here for so long to get these measly 100 S-units. But they're worth nothing until they vest out over ANOTHER 5 years. So at a minimum, you've worked there for 10 years and you have yet to see any financial benefit. But hey, you're making a cool 63k a year at that point so it was all worth it right? It's even shittier if you are single, you know how healthcare is funded by the entire company? Well that's how they justify the lower salaries, yet it's only a handful of people blowing up the monthly healthcare cost while destroying your salary total. At the end of the year, you'll get a letter with your total compensation and they attribute some ridiculous number to your healthcare, when in reality if you are young and healthy there is almost no chance you'll realize any of that value. Do yourself a favor and pass on HP if they start to recruit you. Even if you get hired on at one of the higher positions, you won't vest out for a minimum of 5 years and there is no way it'll be worth the stress and nepotism you will endure to get there.