If you do the tethered jb, you'll be able to install the semi-tethered tweak in Cydia. There's no point in not doing it as a safety precaution. For your benefit, the definitions are as follows:

Tethered - phone shuts off or reboots requires Redsn0w to boot tethered (meaning you need a computer for your phone to boot up functionally again)

Semi-tethered - phone shuts off or reboots but can return as functional without Redsn0w. All jailbreak/Cydia tweaks/apps will become disabled though. But the rest of the device works.

The downside of a tethered jb is obvious. The downside to the semi-tethered tweak is that it won't allow iTunes to sync with the device when installed. But I believe if you uninstall semi-tether, you should be able to sync fine.