You won’t save that much weight with a space-saver, compared to the can-of-goo and 12V tyre-inflator doohickey.
It won’t get you out of every sticky situation that the spare would, but should do most, and many new cars are sold with this.
Also means you can leave your jack and tyre-iron out. 🙂
Surprised a C70 wheel has the offset to work, even in such a limited fashion?