Functional resumes are good when you have little to zero work experience (or new grads). This type of resume allows you to showcase skills that fit in with the job requirements. Fair warning: most recruiters and hiring managers dont like this format and feel as though you may be hiding something. If you have a chronological resume you do not want to have one part chronological and one part functional because it will throw off the entire formatting and may confuse the employer about your skill set.
No sample resumes are accessible. A competent resume writing service will provide a number of samples for review. You can assess the quality of their work only if have these samples. If there are no samples available on their website ask them for the specimens of their work. If they are unable to provide satisfactory examples of their work you had better opt for another service.
If you are currently in the market for a new job having a stellar CV is a must. And while the wording and style you use to write resumes is key you must also have the right format. Some people choose professional resume writing services to get an edge but if you are looking to do it yourself you must have the right presentation to even be a contender.