What are the disadvantages of ADP?

Could you elaborate on the potential drawbacks of utilizing Automatic Data Processing (ADP) systems in the context of finance and cryptocurrency? Are there any security risks associated with these systems? Additionally, how might the reliance on ADP impact the speed and efficiency of transactions, especially in the highly dynamic cryptocurrency market? Moreover, are there any costs or limitations in terms of scalability and customization that businesses should be aware of when considering ADP implementation?