Advantages Of Spiral Model:
Later Stage Changes: Addition functionality or changes can be done at a later stages as proper planning is done at each Iteration.
Easy Cost Estimation: As Prototype building is done in small fragments by which cost estimation becomes easy.
Good Risk Management: As Risk Analysis Stage comes in very early stages and continuous or repeated development helps in Risk Management.
Systematic Development: Delopment is fast and features can be added in a systematic way.
Space For Customer Feedback: There is continuous feedback is taken at each ITERATION.
Large Project Oriented: It is very good model for handling large and Mission Critical Projects.
Better Project Monitoring: Project Monitoring is very "Easy And Effective". Each Phase as well as "Each Loop, requires a Review from concerned people. This makes people model more Transparent.
Disdvantages Of Spiral Model:
High Cost: Cost involved in this model is quite "HIGH" as more planning, prototype version, risk management has to be done.
Need well expertise: Skills required to evaluate and review project from time to time, need expertise.
No Reusablity of prototype: Due to various customization from client, using same prototype for the other project in future is difficult.
Not suitable for small project: It is quite difficult to follow this strategy for Small Projects due to