is still a pre-release feature, even with CB 2103.
Pre-release features are still fully supported features and if you are using an Azure CSP subscription, the virtual machine scale set based CMG is the best choice.
There's no such thing as a "free" subscription really as you will have to add a payment method to the subscription and as soon as you start consuming Azure services, you begin paying for them so it's no longer free. You could certainly use an alternate/additional non-CSP subscription to host the CMG although I wouldn't recommend this necessarily as all CMGs will have to be converted to VM scale sets at some point anyway.