I've used Precision Camera in CT for years. Recently I sent in my SEL18-200 lens that had stopped focusing. To my surprise I got a call from Sony Customer Service, offering me a new, warranted lens for only $50 more than the original quoted repair cost. They seem to have a good relationship!

I've been shooting with Sony crop sensors for about 5 years; first a 6000, then two 6500s, finally two 6600s.
Couldn't be more pleased. I have many lenses; three favorites are the 18-105PZ f4, the 18-200 and the Sony 100-400.
The larger battery on the 6600 is a game changer - you no longer have to have full charge and spare batteries before going out shooting. Both the 6400 and the 6600 inherit the A9 processor and the A7 III focus system. Both are excellent, both have improved color rendering over the original series. Not sure if they're on the 6400, but on the 6600 I use the Control via Smartphone and the S+Q Video quite a bit. I like to shoot birds in flight, sunrise/sunset time lapses and stage shooting when my church is open...