The classic is small enough to just toss on your key ring anyway regardless of which larger model you carry. I practice redundancy with my SAKs not on purpose but because I like so many different modes and enjoy having them with me.
I carry a Swiss tool spirit on my belt everyday without fail for years, if I’m wearing pants I have my Swisstool, I really don’t use it all that often but when I do it’s handy, mostly the large and small flat head screwdrivers and the pliers, the scissors, saw, blade, and chisel almost never get used, maybe a couple times a year, the file also doesn’t get much use as I usually have a better file around and I don’t want to dull it.
In addition to the Swisstool, a classic SD lives on my key ring, mostly just use the toothpick everyday, the tools see little use.
I also carry a dedicated knife, either another SAK such as a Tinker, Spartan, or the wenger variant, an alox soldier get carry time as well. More than half the time though I carry a traditional slip joint as my primary, today is a TL-29, but it’s often a Case trapper, Case stockman, Old Timer 8OT, or a GEC Bunny knife.
As an auto mechanic by trade, I’m never far from real tools, but the Swisstool covers those convenient type situations and frees me up to carry whatever I want without ever being without a toolset.
A two layer SAK is best for me, any more than that and it doesn’t feel right in my hand or pocket.