Different Zextras Backup (export smartscan) and Zextras Migration Tool?

Hi,

I'm newbie here and I want to ask. I'm going to migrate my mail server from old server zimbra 7.1.4 to new server with zimbra 8.6, but I'im still confused between this thread ZxBackup: Incremental migration with ZeXtras Backup - ZeXtras Suite Wiki and this one Migrate Zimbra - ZeXtras Suite Wiki

so what is the different between zextras suite backup (export smartscan) and zextras migration tool? which one should I use?
please help me.. I'm very confuse

Thanks for ur help