Sorry, no, this is not the complete picture.
We have been working on the subscription model for quite a long time, and it's now finally coming. It's currently being rolled out, not everyone can see it yet, it's being rolled out in an A/B type of fashion. But the intention is to make it available to all customers very soon, starting next week actually. It's been a long time coming.
Currently the website is getting an overhaul, and new texts explaining the models are appearing on the website as we speak. The pricing page etc will all be overhauled as well.
To put it very succinctly:
Fixed license key model: looks like EXAM-PLEK-EYIN-HERE format. Is single activation only. So once you activate it, that's it. Can't move it to another server, and hardware/software changes make the license key invalid. If you need to move it you need our help to do it. If you run a cluster, you need a separate license key per server. You also can't change the size of this license key after purchase and activation. This model is restrictive and has serious drawbacks that we want to address.
Amazon AWS tiered instances: on the AWS Marketplace you can launch 5, 10, 25, 50, 100, 250, or 500 size instances. These are licensed automatically directly through Amazon AWS. Also somewhat restrictive, because if you want to change the size after you've launched it, you have to backup your data, launch a new instance of the desired size, and then migrate your data. Also again if you want to run a cluster you need to run multiple servers with such a tiered license on it.
New subscription model: on our website you can make a subscription that you can adjust at any time. It's monthly or yearly. The activation key for this is a long blob of numbers and letters, about as long as this paragraph. It can be activated multiple times, and the amount of connections gets shared between all the access servers that this subscription is active on. So if you buy a subscription for 10 connections, and have it on 2 access servers, you can get 10 connections on server A, or 10 connections on server B, or 3 on A, 7 on B, or whatever combination you can think of. As long as the total is 10 or less then you're good. If you go over, users get kicked off until you meet the limit again. You can change the subscription at any time and increase/decrease at will.
Regarding the question about which is most economical, just ask in the sales department on https://openvpn.net/support
or wait until the pricing page and texts on our webpages are all updated. We're working on it.