Any framework does add overhead, and this is no exception. But Mosaic does a pretty good job of keeping things flowing. All of your API requests are running on totally separate threads with no shared memory to get blocked. The overhead is limited to a native ConcurrentHashMap lookup per tile invocation and the map instance is unique per API request, even when multiple are being handled at the same time. Shouldn’t be a concern for 99% of use cases.

As for the ease of learning, please, give it a try! I think it’s very straightforward but I’m obviously a bit biased. Would welcome good feedback to incorporate into a v1 release.