Xen Orchestra (CE) reports that all my VMs have tools running. XCP-NG Center reports that some of them don’t, and therefore can’t display useful metrics.
I like being able to use both tools since there are some features that are available in each that the other has, and some functions are easier in one than the other.
So, any idea why XCP-NG Center can’t see the tools when XO can?
XCP-NG Center is not something I use or recommend people use as it is not really well maintained anymore.
I have not tried it yet, but one of the features that XCP-NG Center exposes that XO does not is setting the boot order. To me, controlling boot order is a critical feature of any enterprise-grade virtualization solution.
How do you handle that with your clients? What if you absolutely require that your SQL server is up before other servers come online? What about having a Domain Controller come up before Exchange Server?
Does the XCP-NG boot order function even work?
Well to be fair, in an enterprise you probably wouldn’t run your Domain controllers on the same physical host(s), where you are also running your Exchange servers. 
But I agree that this feature should be implemented. And I think it’s funny how they intentionally misunderstand feature requests regarding this:
https://github.com/vatesfr/xen-orchestra/issues/3261
https://xcp-ng.org/forum/topic/1086/xo-new-boot-delay-feature-not-working/8
And here they explicitly say that they want to keep it simple: Auto start VM on XenServer boot
Just one example why I think that Proxmox VE is the better solution for home users and small businesses. For larger businesses and enterprises that are running large clusters, XCP-NG in combination with Xen Orchestra might be a better choice.
XO has a “Start delay” option under advanced that we rarely need to use. XCP-NG scales very well for our large enterprise clients that have over 2,000 VM’s running.