The FAQ for the premium says there is a month to month plan
"Both subscriptions offer access to premium member-exclusive content and Tested sans banner ads and site skins. The main difference between the two is cost. Our annual subscription is discounted 30% compared to 12 months of the month-to-month plan. From time to time, annual subscriptions may also include promotional materials, such as giveaways or coupons that you can use in the Tested store."
But I sure as shit cant find it and I have no desire to receive the art print.
Also I cant find any way to contact anyone on the site? like no support center no nothing? what the hell do you do if you have a problem or you know have a question like this?
I think they removed the monthly subscription a while back, but I might be wrong. I'd shoot an email to the above address and ask, it might be a bug or they might have neglected to clean up the text.