I'm currently using Z51-70. So far this laptop is much better than Z50-70 in terms of features and overall quality (upgraded to Z51 from Z50). Speaker is improved, screen is now anti-glare with FHD resolution. Comes with a nice white backlit keyboard and 2 USB 3.0 ports compared to Z50-70's 1 USB 3.0. However if you go for the base i7 model in which I'm currently using, the HDD is quite slow. Also, keyboard flexing is quite noticeable around the "QWER" key zone and the number pad area. But overall it's a great laptop with decent quality.