I have the B'rel, the Kar'fi and the Bortasqu 3 pack and use them all regularly except for the War Bortasqu. The B'rel is the Z-store purchase I am most satisfied with of all and use the most even compared to Fed Z-store ships I own too like Oddy, Vesta, Armitage, and Defiant.
Only zen ships I have purchased is the modules for the fleet Vor'cha (forget the name), other than that it has been EC purchases, Mirror Universe ships, and getting the time ship out of a box with 18 keys.
I will eventually pick up the B'rel, and then grab the fleet versions as well.
I haven't played with Klingon carriers at all but have throughs of trying that Orion Flight Deck Cruiser some day.