How good Muzishare brand tubes?

Keep the stock tube set! You can probably get two thousand + hours use from the KT88's - and even more from the small tubes! The 5U4 rectifier might be the first to need replacement. Apparently Ch*nese-made rectifiers are not as robust as good US-made GE's and Sylvania's! 

they are most likely rebranded shuguangs

should be ok

agree replace rectifier a good idea

Just got the Muzishare and so far so good. Sounds nice. I will do some tube rolling. First the smaller cheaper tube including the rectifier then later the outputs when i decide which brand.