After a year of recreational cycling as fast as I can then completing SSB1 with about 60-70% compliance (that is actually doing the workouts - I completed every one I did 100%) I managed to bag a 5.8% increase in FTP.
The general recommendation is to do SSB 1 → SSB2 → whichever build program suits you → specialty. I believe SSB2 is the one that you should not skip (I’ve seen multiple forum posts saying SSB2 is almost like a pre build).