I remember trying it like a year ago or so. Even though the graphics is better and more consistent across factories, zk is far superior.
ZK's flat tech tree is a huge advantage - there, you have tech 1, tech 2 and tech 3 units, to build a tech 3 unit you need a tech 1 constructor to build a tech 2 factory, from which you need a tech 2 constructor to build a tech 3 factory, and then you can build the unit - something like that. Wtf.
I feel like zk is more fast paced, which is good. Zk has more units and more variability. All BAR units feel the same. In zk, you have this sumo which has gravity beams, you have firewalker that shoots fire, you have shockley and widows to stun units... In BAR, everything just shoots some kind of laser and feels too similar. Zk also supports much more players, I enjoy those 16v16 lobpots - BAR is max like 4v4 I think. And zk community is bigger.