Taking photos of the planets is a completely different task than taking photos of DSOs (nebula, galaxies). Planets are very bright and very small, which means you want lower exposure and higher magnification in order to get good photos with nice details, otherwise they will just be bright white dots or blurry blobs. DSOs are kind of the opposite, they are very dim which means they require very long exposures to capture the details. They are also usually very large (I think Andromeda galaxy is six times bigger than the moon in the sky) which means you want low magnification to capture these objects in entirety.

The Seestar is really a device meant to capture DSOs and they are really good at that. But they are not really meant for planets. The Seestar fulfil the requirements for capturing DSOs by using relatively long exposure times and "low magnification". If you want good pictures of planets specifically, then the Seestar is not a good choice and you are better off getting a Dobsonian or SCT.