Heathkit was of an era when you could still reasonably build non-toy electronics projects from components without unreasonably expensive test equipment and other tools. It arguably wasn't until Raspberry Pi and Arduinos that we got back to that, albeit at a different level of abstraction.
I'd say between that healthkit and arduino's it was snap-circuits which allowed kids like me to get into electronics, the manual was detailed and looking back it's fairly technical although it unfortunately it always assumed you knew what they meant, the manual would tell you to never short circuit the battery but 7-y/old me was so confused as to why you shouldn't because it never got into things like electron flow.
Way back when I remember having having this kit which consisted of magnetic blocks that were variously switches, diodes, buzzers, etc. that you could snap together to build various types of circuits.
At one point I had something else that was closer to a breadboard (though it wasn't) but as I vaguely recall it had a lot more options but it was hard to actually build a working circuit.
I did briefly get into Heathkit after I graduated school at one point and built a power supply that I still use sometimes but it was pretty much the end of the Heathkit era at that point.
