At least they don't charge too much, you can probably learn to do those SEO activities for yourself, some is ongoing, you would save money if you just spent 20 minutes a day getting the site a few new decent quality backlinks,
Bear in mind a very new site can't add very many new backlinks (the favorite activity of SEO services) without raiding suspicion with the search engines, their first phase services assessment and ion site optimization would be OK, for now your focusing on creating quality original content may be as important as any measure, it would be helpful to have a target list of keyword phrases to incorporate. A store site could add introductory paragraphs to product categories, longer individual descriptions and articles int he main site or a blog, all of this added text gives the search engines more words to match up to searches.
It's best to add backlinks in proportion to the traffic and site age. probably far less than 1 new link for every 10 visitors (assuming in the real world a small percentage of visitors create a link to a site they had visited.) Getting a bunch of new backlinks one week from a paid service, then none the following month tends to raise red flags with the serch engines.