It looks like iEmulator is a wrapper around the popular open sourced emulator qemu. Thus the performance you'll get is going to be the same as plain vanilla qemu, except iEmulator will provide a more user friendly interface. Not hard since qemu is a real pain to install and work with.
If you want something similar to iEmulator that is free, have a look at QemuX. It's still quite slow and definitely much slower than VPC.