Photofilter is actually Photofiltre - French origins.
http://www.snapfiles.com/get/photofiltre.html - good quick description and screeny of it on Snapfiles.
It has some hidden depths, shapes can be made using a shape selection, then applying line & fill, a dew other things are a little counterintuitive, but the freeware version is a decent (but non-layers) editor with no bad habits - can even be made portable http://www.app-stick.com/proddetail.php?prod=PhotoFiltre
Serif Photoplus free does have some bad habits, or maybe some good ones?
It DOES have an ad component, though strictly for Serif upgraded & offers.
Even the free version needs to be registered, and re-registered if re-installed (activation!).
You WILL receive marketing from Serif (software) and their gadget shop, Gizoo, though in many cases, you can stay one version behind, very cheaply.
Serif do not compare well in that respect, to the "greenware" approach of Photofiltre free - no nonsense freeware