If your battery management system has an in-built solar regulator, unregulated solar panels should be connected directly into the unit's solar input terminals. There is no need to install an external regulator between the solar panel and the battery management system.
If you want to add an additional regulated solar panel or a blanket panel, it needs to go directly to the battery. If you want your battery monitor (JHub, Odyssey, Trek, RVView, JControl) to read correctly, you will require a BC300 fitted.
If your battery management system is not solar compatible, then you may install your solar panel direct to battery through an external regulator. If you want your battery monitor to read correctly, you will require a BC300 fitted.