Also, you will not be able to copy a free or paid theme from the Themes page into your Tweak account.
Free accounts have a limit of 2 different Tweaks e.g. for two different shops.
Tweak Plan Information
The Content Delivery Network (CDN) is only available for paid plans. It is used to host any images that your theme may need to use for buttons and/or icons.
The CDN used by Tweak is provided by Akamai through Rackspace and can deliver your Tweak images rapidly around the world - giving your audience a local-like experience, no matter how far they are from your origin server.
These images may be from an e-shop designer Theme you have saved and copied to Tweak, or they may be images you have uploaded to provide your own custom buttons for example. All these images are hosted in your CDN for as long as you pay a subscription.
Having your own CDN, helps users who may not be confident hosting images themselves or do not have secure (https) hosting available as needed by shops running on Facebook for example. With the CDN, you only have to copy the CSS into your Ecwid Control Panel.
If you have not uploaded any images into Tweak, and you have not copied any Theme in to Tweak, you will not be using the CDN and a free plan should be all you need.
It is also possible to get a copy of your CDN contents, extract all the images and host them yourself on your own server. If you do this, you do not need to continue paying a subscription. More information is here.
You can check if your CDN usage for this month and last month in your profile page.
The usage also includes your own usage while using the Tweak pages on e-shop designer.