It is "too good to be true", they don't allow for it:
>Applications using the Map Tiles API are bound by the terms of your Agreement with Google. Subject to the terms of your Agreement, you must not pre-fetch, index, store, or cache any Content except under the limited conditions stated in the terms.
>Applications using the Map Tiles API are bound by the terms of your Agreement with Google. Subject to the terms of your Agreement, you must not pre-fetch, index, store, or cache any Content except under the limited conditions stated in the terms.