So Kickstarter compute blade which is not shipping yet, zimacube which is not shipping yet, or build-your-own for more money which is not really the same category as the zimaboard. Those are not great alternatives today.
Another reason why there aren't that many alternatives is that you can't use it for that much. It's like buying a car that can carry 50 kg. Great if thats your use case, but if you want anything more, there's no point. I can't really use it as a NAS, firewall etc. I think it certainly has uses, they are just ones that the average NAS/server people can do with a stronger server that can also do nextcloud, pi-hole, etc, in one, rather than have a device for each (which is way more costly).