Netscaler WAF Migration

It might be a good idea to follow the feature by feature approach for the reasons suggested, such as ensuring you continue to have the level of protection you have at the moment with the Netscaler WAF, until you have a full migration to the ASM with your policy fully maturing after learning all traffic. Also monitoring the policy building process will allow you to learn more about ASM building your Security policy. However, I would expect that you get more than 75% accuracy on your automatically built policy as compared to the manual built process, particularly since both now use the Unified learning framework, available from v12.x. I believe you should achieve high accuracy with your Automatic Policy builder.