KTVA has its roots in Bel Canto, which is more of a classical style used by many Opera singers.
If you listen to Ken's demos, probably the only one that he has posted that sounds remotely Operatic would be "Nessun Dorma". In that demo, Ken sounds much like the style used by Luciano Pavarotti.
KTVA focuses mainly on a Modern Sound. Some of my earliest stabs at taking vocal instruction included a course from an Opera coach. When Ken first heard me, he immediately started directing me away from the covered sound I was using.
I still catch myself going into that mode if I'm not careful. When I use the brighter KTVA method correctly, I do not cover my sound. The covered sound is a darker, more operatic sound. There is nothing wrong with a covered, operatic sound, as long as you are training for Opera. If you want to sing rock, pop, country, or anything remotely modern, then you need to get away from the Operatic sound. They are two different approaches to singing.
Are you wanting to sing Opera? If so, then go for it!
Are you wanting to sing more contemporary, popular music? If so, then go for it!
These are two opposing training methods. They share many common points, but the vowels and the coloration of the sound are totally different, and like two different languages in many respects. You can't do both simultaneously. When you are doing one, you have to do that one completely. And likewise when you do the other. Where they converge, they converge. Where they diverge, you may run into problems.
KTVA uses vowels from the English Language, and carries chest voice far above where opera carries the voice. Opera does not pursue head voice for males, either. Opera utilizes only Italian vowels.
We literally ARE talking two different languages here.
Figure out what your vocal goals are and take the most direct and logical approach to attain them.
Good Singing to You, Ken Jack!
Ken sings arias here and there when he wants to, and he does a good job.
His vocal method is more about Modern singing. He is perfectly capable of training you in Operatic style if you want him to.
For the most part, his students want him to teach them to sing modern popular singing styles, and for that he needs them to sing without the covered sound and without the Italian vowels.
So if you are fluent in both styles and want to sort out and have both Metric tools AND standard SAE tools in your toolbox, I think that's fine.
You probably don't want to mix your brain surgery tools in with your automotive tools, though... That probably would be a good place to draw the line. Just kidding!
If you are coming into KTVA with a classical approach and keep the baroque with the baroque and the baROCK with the baROCK, you will do just fine. It's just not likely that there will be a lot of KTVA videos and updates on that portion of your interests. If you do webcams with Ken, however, he will be glad to work on whatever you want to work on.
It's all good!