WE Hi-Capa's are great if you can find one that is reliable out of the box. Sure the lemon rate is higher than TM, but WE standards are improving.
The WE Hi-Capa provides a cost effective metal slide option right out of the box which is nice. My WE has seen a few thousand rounds and never let me down, that isn't the case for everyone, but like I said if you can get your hands on something reliable you're good to go.
The 100 % TM compatibility on the WE Hi-Capa is a bonus that you wont find in the WE 1911A1 or MEU.