Francine,
I have been using PithHelmet for several years and am quite pleased with it.
There are a multitude of settings, many of which are arcane (IMNHO), but the default settings work just fine. As you grow more familiar with PH, you may care to then tweak the settings.
With each new version of Safari, PH ceases to work. There is an easy fix (hack) if you must have PH working instantly, but many just wait for the developer to release an updater. Usually, this is a few days after the Safari update.
FWIW, I would go ahead and delete the old SIMBL version as suggested. But if you are still uncomfortable with the installation, you may care to
Email The Developer And if you haven't already,
This Page has recommended reading.
And finally, make sure you have the 10.3.9 version (it's linked on the above page).
HTH