Those spice balls really constrict the hops inside unless you're using a very small amount.
Now that being said, the strainer/hop bags aren't exactly 100% effective at their job either. I just brewed a black IPA w/7oz in the spider. When it came time to xfer the wort to the carboy, I had to filter out probably 1oz worth of hops. That's all the finer material that slowly makes its way through the micro-holes in the bag. But it's great for just removing hops at the end of a boil and not dealing with nearly as much a mess during IPA brew sessions.