The choice is yours. You can try out sample applications, Break Caldera, connect your Metamask, or deploy your own dApp on the platform.
No, these testnet rollups are completely free to use.
Yes, the rollups run on a temporary testnet L1, but they are fully functional and store data. The technology used for the testnet rollups is the same as that used in production in mainnet
To use the testnet rollups, users must authenticate through a Magic Link and can only have one active rollup at a time. These testnet chains are temporary and will expire 12 hours after deployment.
Please note that the funds on the rollups have no actual value and it is not currently possible to transfer external tokens to or from the testnet rollup.
The level of customization is limited at the moment but will be greatly expanded shortly. See Chain Customization for a full list of planned customizations.
Bridging functionality between the underlying L1 and the rollup will be exposed soon (via a web UI and SDK).