Most fiberglass rods are parabolic. That means it bends throughout the whole blank, rather than shutting off or having a defined backbone. Non-parabolic rods would have, for example, a really soft tip and then lots of backbone, like a graphiter. Since the sticks we're talking about are 10ft. long, they don't really need a backbone because they're so big that it takes a lot of pressure to put a parabola in that blank all the way to the handle... There are advantages and disadvantages. Parabolic rods kill fish pretty quick, but they're also tough on the angler. Especially 10ft. of em. A good sized yellow will ruin your day. But, if you're hardcore enough you can turn em quick and put the hurt to em. That's sort of the fun with the big jigsticks, you gotta grind on em and pull as hard as you can and hope you don't get your @$$ kicked. Parabolic jigsticks also toss jigs pretty well. Since the blank flexes pretty far down, it'll launch the jig pretty far. When you cast a parabolic rod though, it's more of a slow, sweeping motion rather than a full on jig huck. I couldn't tell you whether or not my 540 is parabolic or not, but it doesn't act like it. There's no way I could put a bend in that rod all the way to the handle if I wanted to. So, I fish it like it's not parabolic and just huck em. I think the Harnell 542 is a little lighter and flexes a little farther down the blank so you have to sweep rather than huck. Those Harnells and Trulines are oldschool, totally awesome rods. I will definitely be buying at least one of each sometime in the not so near future.
-Brian