Thunderbolt Duo 4TB for iMac as boot main drive

Owning iMac 2012 and would like to use new Thunderbolt Duo 4TB as boot main drive and will disable internal HDD.  Would it be applicable and any speed different?

Check the link below

Hope this can help

http://wdc.custhelp.com/app/answers/detail/a_id/1787/session/L3RpbWUvMTM2MTQwNjE1Mi9zaWQvUEE2UEZtamw%3D