I owned one. Great canter, OK walk/trot, decent mind but VERY alpha. He was a kicker and a bucker.
I could not keep him sound. He always was NQR. Perhaps that explained his issues u/s.
Mine was a TB cross- with a very nice approved mare that had dropped some lovely foals. My Viva was heavy-boned and more of the old school type WB even with TB on the bottom.
I do like the G lines as a rule, but not sure I would own another Viva. Just anecdotal on my end though.