Can't say much on the link for that template since it's now done
by us ( I may only suggest you contact the site owner for that).
Google has had that test available a while ago .. and though useful,you
shouldn't read that much into it.
Responsive sites seem to be all the trend nowadays, and although it IS
necessary to cater for mobile devices, it will be a long way till all
sites are built with that in mind. ( and, of course, you need to
convince clients with non-mobile friendly sites to pay to
upgrade/rebuild their sites!
Even BIG company sites are not "mobile" friendly ...(yet) !
To being with, the product must actually exist in your database ( so
that the cart knows the products info + price).
I'd recommend checking the generated source for the product template
( when visiting the product you need), and copying the HTML form that is generated.
In any case, I would recommend that you convert your site to .php
throughout, so that all cartweaver code can run anywhere you need it to.
Otherwise. yuo may run into issues when specific pages need to parse PHP code.