Hellwig bar gets a big thumbs-up from me... enough to inspire my first post! I have to say I'm somewhere in the middle of the pack in terms of subjective response. I am noticing a good improvement in handling (vice those who claim to notice no difference), but not when just tooling around city streets (vice those who seem converted after pulling out of the driveway).
The biggest change has been through medium-to-high speed cornering and changing-radius turns. My 02 4x4 AC tracks MUCH truer and holds a set MUCH better than before installing the bar. The "wallowing" sensation through corners has disappeared almost entirely. If I had to summarize, I would say my tallish truck now corners a lot more like an unmodified modern sports sedan (think Altima or Camry) than a truck. That's a big improvement. Tremo's install guide is a must, BTW. The install is fairly straightforward (certain steps inspired curses and invocations against the bar's engineers, i.e., driver's side "square bolt plate"), but the additional help from Tremo is invaluable. The suggestion about preinstalling the end links PRIOR to mounting the L-brackets is worth a lifetime subscription to TS, all by itself!
Plus, I can now at least keep up with my girlfriend, AKA Leadfoot, in her 05 Corolla S. If you are thinking about these, stop thinking and just order them.