Think of LifeBalance as a replacement for the "Tasks" application that comes with the Palm. It doesn't replace your calendar or contact manager.
If you're not a Palm user at all (you mention Mac but not Palm) then you could use LifeBalance as a Mac-only to-do list manager. You'll still need iCal and Address Book.
I use LifeBalance on a Mac at home, a PC at work, and a Palm everywhere. It syncs smoothly between all three platforms with no glitches so far. I switched to LifeBalance from the native Palm Tasks list for two reasons:
(1) The Tasks app is limited to 16 contexts, whereas I use about 26 contexts at present.
(2) LifeBalance supports hierarchical lists of tasks, sub-tasks, sub-sub-tasks, etc. (8 levels deep), whereas the Tasks app is "flat" -- no sub-tasks. This better supports the way I think about my projects -- I like to break tasks down into subtasks until I hit the right level of granularity for me.
On the downside: I do miss the simplicity of an all-in-one PIM -- Palm Desktop for Windows is great, on the Mac it's a horrible mess (why oh why couldn't they implement the app the same way on both platforms?). And I hate iCal on the Mac too, so at home I tend to stick with the native Palm calendar app.
There is a 30-day free trial download of LifeBalance, why not try it for yourself?