The reason why we recommended those is simple: The investment cost is so small, that even if you don't like what is produced, and if the seller can't or won't fix it, you can always drop another $5 and get a second take from someone else. Worst case scenario: You lose a latte.
But there are some services on these sites that you really should not purchase. These include:
Website content. Law firms' website content is mostly specialized -- you need to know law to write good legal content. And to write effective legal content that ordinary folks can understand, you need to be a good writer and understand the law. You're not getting that from a $5 stranger.
Social media followers. This is just sad. Would you buy friends in real life? There are many ways to gain followers (follow other experts, write intelligent things), but buying fake followers isn't an effective one. Sure, you'll have like 24,154 followers on Twitter, but with six tweets and no interactions, your ruse will be quickly uncovered.
A professional-looking website. These are microtasks for nominal fees. What kind of website can you get for $5? Will it look professional? Will it be responsive? Will it be optimized for converting visitors to actual clients? I may be wrong here, and maybe someone in a foreign country can build a damn fine website for $5, but I sincerely doubt it.
SEO. Some promise links. (Typically, more links to your site = higher Google search rank.) Some promise positive "social signals." For the most part, these will hurt more than help, as Google will nuke your site's ranking when (not if) it finds out that you have fake spam sites linking to you. (And for $5, that's all you're getting.)
Of course, this is the point where I highlight that yes, FindLaw does do lawyer marketing, SEO, and websites. Sure, these services cost more than $5, but once in a while, you actually do get what you pay for.