I tried a quad stand and hated it. The reason being I like my monitors curved towards me, not flat but I didn't realize it till after trying the quad out.
Using a 6 screen flat mount would mean a lot of screen real estate completely flat. Seeing from side to side would look like a tennis match, which is fine if that works for you. For me, I wanted my monitors curved towards me.
Even if additional stands are a bit more bulky, I love the setup of having independent dual stands.