the Zoom B2.1u does sampling rate at 96kHz, that's pretty high, so i shouldn't sound too bad.
Depends on what you want.. if you just want non nonsense overdrive or distortion and only want 1 effect, then get a single pedal.
Multi-effects offer more functionality - the zoom has a really good and fast tracking Tuner built-in, modeling, simple drum machine for practice, effects, EQ (normal and parametric EQ), delay, octaver, chorus, overdrive, distortion, reverb, flanger, etc etc.... lots.
Some you may like, some you may not like, but it's all up to you what sound you want. Some people say the Zoom effects don't sound good, some people think they sound really good.... it's all subjective...
different people have different ears, so the most important is to sound good to your ears.