I took a look at the mobile page, and here are some of the things that struck me. You said that the majority of your traffic is not on desktop, with 2 out of 3 visitors using mobile or tablets. That fits with a lot of the sites that I'm seeing these days.
Research seems to show that mobile users consistently move from one device to another during any single day. They'll research on smartphones, but then tend to move to another device when purchasing. Typically, conversion rates are 2 or 3 times higher on desktops than on smartphones, which fits with what you're seeing. I myself generally move across 3 devices during the day, but buy 90% of the time on the desktop.
Here are a couple of links for background on this.http://www.smartinsights.com/mobile-marketing/mobile-marketing-analytics/mobile-marketing-statistics/https://ssl.gstatic.com/think/docs/mobile-path-to-purchase-5-key-findings_research-studies.pdf
So I'm kind of thinking that it's important to get them a smooth mobile experience, and to make it easy for them to pick up the thread again on the desktop.
I don't know how easy it would be to add a mailto link/button to the mobile page, which would open the default email program with the link for the page already in the body of the mail. The visitor could then send themselves an email link to read later. Might be worth investigating.
There are a couple of things I'd consider if this was my page.
I like the image at the top - very good. The gallery is very effective on the mobile, although I found it less intuitive on the desktop. On desktop, I couldn't see the arrows very clearly, and there's a disconnect between the thumbnails and the image itself. It might be because they're not centered under the image, but it took me a couple of scans before I realized it was a sliding gallery. It's easier to "get" the layout on the old version but overall, I like the new version better.
After the introduction, I'd be tempted to put a bullet point list of jump links down the page. This would give an idea of the length of the page, as well as the opportunity to jump down the page. It would depend on how long the list became. If it was too long, that wouldn't be good.
Personally I'd move the testimonials to the end, so the page flow would read
Make My poster now
Example poster wording
Printing your poster
Framing your poster
I can see why you have the testimonials at the top, establishing trust etc, but on the mobile it's stopping me seeing more information about the product. They're quite long, and it's only on the fourth swipe that I get to more information. The blockquotes also don't look quite right on mobile. They're a bit thin, which make them awkward to read, and they're longer than they need to be, but that's just a CSS thing and easy to alter.
If having the reviews at the end is good enough for Amazon, it's good enough for me, lol.
Like AJ, I find it odd that there is so much focus on the desktop view. Generally, more visitors arrive onto your site on mobile, and it's the first touch point. Google says the SERPS will become mobile first eventually. Putting it another way, this afternoon's mobile visitor is this evening's desktop purchaser