That is what the makers say, though not having used them myself I can't vouch for them. 

Fixerlabs has a service that's reasonably priced where they will upsample an image for you, and give a coupon so you can get the cost back if you purchase SizeFixer. That might be worth trying out.

The Genuine Fractals site has a fully functioning demo download that apparently lets you do 20 images before ceasing to work so that you can evaluate it, here:  http://www.ononesoftware.com/download.php