The T3 Full Spiral bulb originated when end users started to complain about the traditional U-Shape CFL bulb not looking "like a regular light bulb". The spiral shape gives the light bulb a more pleasing appearance when you look at it (not that you should be staring directly at light bulbs) and is physically more compact.  In addition the T3 Full Spiral is known to be:

• More economical than a T2 Full Spiral but more expensive than a T3 U-Shape
• Capable of achieving 10,000 hours of lifetime
• Available with a wide range of quality certificates for almost all countries
• Commonly used in residential settings