So, if there is no real difference, what is the advantages/disadvantages of smaller soapbars (emg/spector style) and exposed-pole MM style pickups
Ah, so the gates are open.
There
IS a real difference, but you need to understand the following:
-
Visible poles are an
aesthetic thing - it's irrelevant to the sound. There ARE exposed-pole EMG/Spector style soapbars, and there are MM style pickups with no exposed poles.
-
Shape is irrelevant, but NOT because they'll all sound the same - it's because
it doesn't tell you what the pickup will really sound like.
-
The position of the pickup on a bass is important to how it will sound. Any MM pickup, placed in the "sweet spot", will sound different than the same MM pickup placed close to the neck.
And then, the punchline...
Different pickups sound different, even if they're the exact same shape. But it's not the shape or the housing - it's the design of the pickup itself and the circumstances it's placed in. The way it's wound, materials used, active/passive preamps that color the pickup's natural tone, its position on the bass, the other pickup(s) (if it's a two/three pickup bass), etc....
Now that I have the "sound" issue out of the way... there are a few real advantages/disadvantages of just the shape alone.
Off the top of my head... MM pickups are huge, and as such, having two of them on your bass (like on HH Stingrays) can really get in the way of slapping and popping. So can smaller humbuckers, but you usually have a bit more space to work with. And regarding exposed poles (like what you see on most, but NOT all MM-style pickups), they might develop a little rust over time. But you can clean that off.