Just an opinion, so it is not worth much but…
If you want something in ZS or a bug fixed, you could try implementing/fixing it yourself and then send the changes to Fulvio.
In my case, ZS looked to be the closest router to my needs with multiple WAN interfaces and support for VoIP (SIP/RTP). I also happen to have a couple of public servers on my LAN and wanted QoS so that mail/web traffic would not affect VoIP quality.
But I found some issues with the interaction of QoS and NetBalance. I dug in and fixed it well enough for my needs and sent the changes to Fulvio. Later, before Fulvio released another beta, there was some interest in my changes and I found that my changes were not enough to solve the similar problems others were encountering so I have revised them and re-submitted to Fulvio.
I must say that Fulvio and ppalias have both been most helpful in considering my changes and helping test them. Those changes are still in a bit of flux while more testing is being performed and users on this forum indicate yet more network topologies that I had not considered. But I do expect that the next beta will be better in regard to QoS and NetBalance than the previous one.
That was the area that I was in need of fixes and I was able to contribute. So if there is an area that you need improvements and you have any ability (or lack of fear), dig in and submit the changes for consideration.