the suck switch is on the Hagstrom Bisonic pickup equipped basses (1960s), and has basically no value. it is not really the “switch” per say that sucks...it is the trasformer/choke inside the pickup cavity, it just needs to be bypassed. from there it can be modded further, and the actual switch made usefull, but just bypassing that choke under the neck pickup is the real issue.
On the Guild Humbucker equiped basses (1970s) the humbucker in standard position sounds great but is super hot. the quintesential 70s mud of the power trio. with the deep/hard switch engaged it cuts alot of the heat and sounds closer to a Fender bass tone, but it cuts like half of the signal- turn that up and it sounds fantastic...just dont hit the switch back to fat/mud (intentionlly or not) while its super loud in “Fender mode,” as that could result in an apocalyptic explosion.