There was nothing special about Hilux springs apart from the fact they were available and suitable (same width, and appropriate extra length). But this was over 10 years ago, and there are a lot more springs to chose from these days (because a lot of dual cabs still use leaf rears) and they have better "technology" in the design of the leafs and packs. So if you're going that "hardcore" mod route (beyond bolt-in), I would be looking for better alternatives, front and rear. You might even be able to pinch some lightly used stockers out the scrap bin at ARB or something!
There was a thread where I rummaged through various catalogues trying to find good options, but I can't remember the name of it. I remember that user Baja Burley was interested in doing spring swaps at the time, which is why I was looking, and he eventually did do a RUF, then use hilux springs. You might have seen his build thread?
Baja Burley's truck!!
There was an even older forum called Outerlimits4x4, and there were some blokes/threads on there that did some pretty hardcore suspension mods (which is probably where the initial idea of hilux springs came from), but that forum is long dead.