The SC/MP seems to have been more popular in the UK than in the US. For example, Kilobaud #1 mentions only three CPUs--8080, 6800 and 6502. I remember looking at the datahseet for the SC/MP and shaking my head--awkward addressing (16 pages of 4K a la PDP-8 ) with very slow (multi-cycle) instructions.
The other problem that dogged National was the world trying to figure out what the heck they were trying to do. This was probably Charlie Sporck's fault. NSC started with the IMP-16 multi-chip microprocessor, followed by the SC/MP, followed shortly by the PACE, which hailed back to the IMP-16. At the same time, they were aggressively second-sourcing Intel's 8080. I suspect they spent more money on developing the 8080 development system (NSC Starplex) that they did on the entire SC/MP program. Then they were second-sourcing the 8086, then trying to sell their NS32K chips (a great design, but they let Motorola and Intel grab the market, all the while telling prospective customers "Real Soon Now" and then following that with buggy silicon). Somewhere in there, they were peddling the NSC800 -- a Z80 in 8085's clothing.
I think any engineer worth his salt would have no qualms about using NSC's linear products--they were legendary. But National never did seem to get the gist of what the digital world was about.