Most people purchasing a cloud NAS are not aware they are being charged twice; once by the cloud provider and once by the NAS vendor. It is important to understand how you are being charged for a cloud NAS.
I've looked at the responses from your most recent contributors. All make excellent points.
My concerns would be reliability, company reputation and history, seamless integration into existing environment and userbase, excellent customer references for service and support, exposing all costs, features that offer protection such as immutable storage and single, foolproof global file locking, high availability features, user self-service file restore, automatic retention enforcement are all important items that I would look at.
The rest, such as support for needed protocols, speeds and feeds,
It very easy to manage via webmanger gui
it offers a global biew on what happen by host, pools,
Create,delete , expand & reduce,migrate pools is very easy like kid game.
waht i liked on it, its cababality to add external storages (another nas) and manage mdisk and pool from one webinterface
A NAS System for me, has to be seamless integratable in an exsisting Environmend (such as Microsoft Domain Services), so it is important that the OS of the NAS supports CIFS 3.02 with Server Site Copy Offload an other native MS Windows Server Features.
I don't care very much about the (afaik often manipulated) Opinion in Forums and Blogs!
Thats why i agree with Chris Krikke. It's more important for me to use a reliable Hardware and Software Platform with depandable Service Levels Agreements, than any "cheapo" Hardware and "self-build" or "Open-Source" Software from shady Sources...
There are the common answers like IOPs, throughput, bandwidth, latency, etc. What I do is look for end-users that are happy with the product through blogs, forums, articles, etc. it's too easy to get lured in with marketing hype but real world experience from somebody that has actually been using the product is invaluable.