What's the difference between fixed pitch and collective pitch helicopters?

Fixed-pitch helis change altitude by spinning the rotor faster or slower and are simpler, cheaper, and more forgiving. Collective-pitch helis change the angle of the blades, which enables aerobatics including inverted flight, but they are unforgiving in a crash and far less beginner-friendly. Reviewers we read recommend starting fixed-pitch (or coaxial) before stepping up to a collective-pitch machine like the Blade Fusion 360.