Questions about performance degradation when used with DNS features in GTM solutions

Using dns express as a slave dns server, but dns express has a disadvantage that it does not perform recursive queries(such as NS or cname, recursion will not work if a request is made for a delegated sub-domain if the parent domain exists in DNS Express)  and needs to be combined with iRules. When performing recursive queries, disable dns express and roll back to the bind function for recursive queries