hmm, from what I know single product websites don't have a lot of keyword to target, so you gotta use every bit of help you can get.
I would say, do all of these...
- use EMD... or at least perfectly clean and topically relevant expired / non-dropped domain (if you can find one)
- find at least 50-60 (preferably long tail) keywords you can target, even if they're not very related to your product (they need to be at least remotely relevant, though) and start blogging on those keywords...
- optimize the crap out of the content, and interlink all of the extremely relevant cluster pages together
- make tutorial videos on using that product, and publish those videos on your site and link them to your YT channel (of course, you do need to create a YT channel for this first)
- also use a lot of screenshots, stats, graphs, etc of the product in your content (basically, craft your content in such a way that no stone is left unturned about the product and that your visitors will see and know everything about the product, inside and outside, just by seeing those images)
- make infographics on the product's pros and cons, benefits, features, best uses, etc and submit them to visual sites (Pinterest, Imgur, Flickr, DeviantArt, etc)
- participate in UGC sites and specialty forums (Reddit, Quora, Stackoverflow, Substack, etc) continuously (make it a habit to spend at least 30-60 minutes a day in each important UGC site like Reddit, Quora or Pinterest to participate in discussions related to your product / your product's type / your product's category / your product's niche... and, of course, have a link back to your website in those discussions if the rules of those websites allow, otherwise use the link in your signature / profile)
- run PPC ads in various sites that you can afford. If your product lacks keywords to make content on, probably that you won't be able to rank since you might encounter google penalties like "thin content". And if this happens, instead of wasting money on SEO for 6 months like you did, it might be smarter to invest that money into other means of getting traffic (PPC being one of them) and then, when you will have acquired a constant flow of traffic, google might see this and start rewarding you with rankings anyway (google loves not being left out of sites that are popular / important to people, so they tend to rank those sites despite of all SEO rules that they might, or might not meet), so it pays to build traffic outside of google, and PPC / advertising in specialty forums, UGC sites, other advertising networks (Revcontent, Infolinks, Advertise.com, BuySellAds.com, etc) might pay off where SEO doesn't