Personally I have not used Window Washer so take what I say with a pinch of salt
Personally I would not pay for something like Window Washer when there are perfectly good and free solutions out there.
Window Washer provides a much larger range of features than Erase but with a little work you can get eraser to do pretty much all window washer can. Personally I think Window Washer is more comparable to CCleaner.
Windows Vista Compatible: eraser, ccleaner can do this. dban is OS independent. Extensive Wash Areas: CCleaner can do this, eraser with some work can Browser Activity Eraser: CCleaner can do this, eraser with some work can Permanent Bleaching: CCleaner and eraser can do this Free Space Cleaner: Eraser can do this One-click Shredder: Erase can do this. Critical File Protection You can set up file protection with CCleaner* Smart Cookie Saver: CCleaner can do this Flexible Washes: CCleaner can do this Automatic Wash Cycles: CCLeaner and eraser can do this Total System Erase: DBan can do this Expert Customer Support: Support for ccleaner, dban and eraser provided by user forums.
*It is worth noting that while CCleaner can do this, eraser will not honour the protection.
As I've said before I've not used Window Washer but I've heard a number of reports of WW actually failing to securely erase files and leaving them to be easily recovered.
Ultimately I'd suggest saving your money and going the free route.