Do you know any peers or even family members you trust implicitly to look over your app several times? I get the allure of an app review service but my WAG is that the majority of successful applicants to Delta didn't use one, myself included. Personally, I would use it as a last resort. However, if a service like that is included in an interview prep course/service then by all means.
I'm not trying to be a smart-***, just pointing out a way to maybe help you save some coin you can put towards your blue suit and red tie
