The SPIW programme ran from the roughly late 50s to late 60s and was aimed at producing a revolutionary military riflle, including sabot fired flechettes. It failed.
As for your acquaintance, yes, some makers offered flechettes in 12-bore, and buckshot with wire between the pellets, and weird loads that shoot fire. Some still do, in the US. But, basically, they are gimmicks. The kind of thing that a Walty SPAS-12 owner might like, given that the SPAS-12 is arguably the most Walt firearm ever made.