Is a dual extruder a reasonable choice for all-purpose printing
Not an expert by any means but I can’t see any reason you couldn’t use one half of a dual extruder. The benefits of not using one though would be decreased extruder weight. Especially given that this is a direct drive so there will be two stepper motors I believe. Reduced weight means faster print times and a reduction in certain print artifacts such as ringing etc.

Short answer, if your only ever going to need one extruder probably avoid a dual but if you want the flexibility this should work when a single extruder is required.