bio balls are good for what they do like any part of a good system they require maintinence, periodic rinsing to keep them gunkm free.
Pros: the high surface water to air interaction allows offgassing of ammonia which in turn leaves less in the system to break down.
easy to set up, bio ball systems are usually pretty much plug and play.
maintinence is simple, put in bucket of tank water rinse put back in filter.
helps provide good air exchange for oxygenation of your water.
Cons: if not maintained can be come a place for detritus to build up causing high nitrates
has to be cleaned periodicly
only provides areobic bacteria growth where LR provides areobic and anaerobic bacteria growth.