Image Science vs. RMagick

I'm looking at possibly going with Image Science (http:// seattlerb.rubyforge.org/ImageScience.html) for an application in development. I've heard that it is a lot less overhead than RMagick and we really don't have any complex image requirements. Are there any folks out there using Image Science that could chime in with some feedback? Also, I have a couple specific questions:

1. Can Image Science dynamically create images without creating files in the filesystem? For example, if I want to dynamically render an image with different size constraints but only want the original file in the filesytem.

2. Can Image Science apply any compression to .jpg's?

Thanks, Tom