Are the others scams, legitimate third party resellers or "added value" services?
- http://www.applyesta.com/ (defunct - domain is for sale circa 2020)
Can anyone confirm either way?
Updated 2020: The above have better "not affiliated with the U.S. Government" warnings now, but beware there are newer more sneaky sites starting all the time:
And fortunately more official guidance about this issue: https://nz.usembassy.gov/be-aware-of-esta-scams/