Does the DNSBOX master appliance allows zone transfer to their existing Linux BIND and how we can do this from the DNSBOX300/400

They could do this from the DNSBOX300/400 DNS > Server page. Edit the localhost by clicking on the pencil icon.

Then, under the Allow the Transfers To, they just need to add the Linux BIND IP addresses in the box and the Zone Transfer will be allowed from the master appliance to their Linux BIND server.