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