Do you mean Project 82?
Not myself as I've just used clipleads and whatever caps/resistors I had on hand to do it back when I played with passive designs. Now I build everything active I don't bother.
Unless you are doing a lot of speaker testing and development, I'd just use clipleads. Also note the article is from 2001 when software based measurement and development tools were expensive and rare. Today a suite like ARTA would cost less than the box would to build and will do a whole lot more as well.
The free version will do everything except Save I believe, which you can get around to some extent by using a screenshot.
I don't use it myself, but struggle through Soundeasy instead. ARTA was suggested as it's quite inexpensive considering it's capabilities. For subs I wouldn't bother with a Zobel, but for designing multi-way main speakers you are going to need a measurement suite of some sort anyway.