I suspect the Whisper Junior is just the old name for the Whisper PF-10. The name of this product (in fact the whole family) has changed a couple of times over the years, but they all use the same physical media. There are two sizes: junior for the smaller filters and regular for the larger ones. I use these particular junior filters for my PF-10.
2 x Goldfish - $0.09
2 x Ghost Shrimp - $0.60
Look on wife's face when she found out how much I've spent on fish related gear this month - PRICELESS