Yes you need to work a public service job for 10 years which includes government, non profits, most hospitals, and universities. This means that rather than being a limited option, the scope of the program is rather large. Many Government jobs, from what i've seen, have decent entry-level pay and strong benefits.
With this program you pay back a percentage of your income, not a percentage of the final loan. So, if your income is less, you pay less. If you are banking, you pay more.
The key thing is that you are not paying a % of the total loan. The amount payed back in 10 years will vary by income, but people who already have 20 - 30k in graduate loans (or who will have this amount by the time they are done) should take advantage of the need-based increased loan amounts for public health graduate students at a CEPH accredited institution
Most graduate students are capped at 20,500 a year (or 10,250 a semester).. more if you go during the summer. Still, in todays world that may not be enough to eat, pay rent, and get all your graduate work done well. For myself, need-based loans means I get about 6k more a year than standard graduate students (about 25k a year, or up to 35 with summer) That combined with the forgiveness program means I'll be paying back only as much as I would have by taking standard loans (since I already owe a good bit).
If I were to take 10k a year or 35k a year the payback will be the same.
While I caution against getting loans to most people, in this case there is a very strong financial program available to help you pay them back, live, and succeed in graduate school.