I have taught at one for 8 years and interviewed for the other.
I can confidently say even though the teachers at Ngo and Sons may not have the same credentials as those advertised at Matrix, they have trained to a very high standard. Ngo and Sons emphasises rules and technique over everything else.
My brief interaction with Matrix suggests they are more focused on social interaction.
I'll let you pick your slice of the pie - you should definitely trial their classes!
(I wouldn't address Mr Mai as David Mai but if you do, I'd like to hear the recording
)