I have them and they work great in the front loading bobbins. I haven't noticed a difference in the top loading bobbins. They do last forever. If you want some, maybe you could split the bag with someone? The price is high for what you get, but they last forever, so worth it to me.
You can order them online here:
http://www.keepsakequilting.com/productdetail/8248.htm
or ebay or several other online quilt stores. They are about $10 a package.