All marketing is marketing that will land on flat ears. In the end, you'll have to try System Initiative, see if it is a fit for your use case today, and if it isn't, if it's worth paying attention to tomorrow. I wouldn't (and you shouldn't either) make a technology decision based on what anyone says on their website or blog. :)

Today the obvious drawbacks:

* Terraform has tons of coverage in their provider ecosystem, and we're not close to that yet.

* We have some enterprise features still to add.

* There is some work to be done around huge infrastructures, both in how to provide easy ways to visualize them and how we scale the underlying graphs.

https://docs.systeminit.com/roadmap/

We have plans for all these things, but it's early days. My advice (not just for SI) - you should always build representative prototypes if you want to understand what a technology might do for you. Your circumstances matter, and your problems are likely unique.