I really can't imagine owning an electric guitar without one. There is so much that can be added to a song or a solo with the discrete use of a Tremolo, that can't really be done any other way. There are basically three variations / styles:
1) Fender --- I haven't owned a Fender guitar for years, but I was never really a fan of their various tremolo systems. The ones I used didn't stay in tune well, and they don't have a very wide pitch range. Good for some subtle shimmer / wavering, but not much more.
2) Bigsby --- their roller-style tremolos are okay for adding some "shimmer" here and there, but not much more. They're also notorious for reducing the amount of sustain. They're very easy on strings (no stressing across a fixed bridge) and also easy for changing strings, comfortable in the hand, and require very little adjustment.
3) Floyd Rose --- the Floyd's offer the greatest amount of pitch change, usually being able to pitch up 5 tones, and down a full octave. The strings can be locked down in the Floyd itself, but a locking nut or locking tuners are a necessity for tuning stability (I prefer Grover 106 locking tuners), because a locking nut requires making a few holes in the headstock joint, which ultimately weakens it. The Floyd's are also hard on strings, as they're being stressed across the fixed bridge every time it's used.
A few years ago, a machinist named Eric Stets came up with a tremolo design, that could retrofit any guitar without any modifications to the guitar itself. Our own Russell Harding first introduced them to us several years ago on Chordie, and I'm glad he did (thanks, Russ!). The "Stetsbar Pro II" has similar range to a Floyd, but the bridge floats with the strings so there's no string stress. They simply bolt into the existing bridge holes on most guitars with ease. I've retrofitted a few guitars with them, and we agree that it's the best of all worlds. I installed one on a Gibson SG for a friend, and the extra few ounces of weight pretty much eliminated the imbalanced neck-nose-dive SG's are known for. Add a set of locking tuners, and you're all set.
Online Review: https://www.guitarinteractivemagazine.c … o-system/#