such a disappointment on tp-link i feel cheated as the product page got qos http://uk.tp-link.com/products/details/cat-4691_TL-MR6400.html#specifications
purchased the product but found no option for QOS on 4g/3g router working mode option...

Yes, I am also one of the victim!!
I have sent an email to ask my local customer support regarding the missing QOS feature.
And this is how they replied me. :mad:
Just said sorry and that is all. :mad:

I definitely feel cheated as on their product page clearly said that it has QOS feature... I also contacted support and they also reply with the typical "sorry" . I cannot claim on exchange with my the retailer i purchase from..... http://uk.tp-link.com/products/details/cat-4691_TL-MR6400.html#specifications

Sent email to support.my@tp-link.com and told them about it as well, they explained that the MR6400 only support Bandwidth Control in Standard Wireless Router Mode. And said they will change it on the website ASAP. It seems that the 3G/4G mode cannot control the traffic:(

TPLink can't be trust any more.
Let's move to other link.