Just like using the sling, I've found that my action has to be quick when using a mei tai, before DS becomes impatient.
I have used the sling since the 2nd month, and the MT since the 4th month. I am still using both.
To the contrary, DS likes the MT quite tight (snug fit). If it is too loose (e.g. so low that his bottom is below my tummy) he will fuss. Tightness seems to give him security. If it is too tight DS will let me know, so I am not afraid if I have squished him.
My trick: when DS starts to fuss, I make a few bounces and cheer him up. It usually works.