Yes, you can use the Full Swing KIT indoors. However, there are a few things to keep in mind. First, you will need to make sure that you have enough space to swing freely. The KIT requires a minimum indoor room length of 21 feet, comprised of 10 feet tee-to-screen distance, 10 feet tee-to-launch monitor distance, and 1 foot behind the impact screen. Full Swing do not advise minimum room width and height requirements, but I recommend at least 10 feet width and 10 feet height.
Second, you will need to make sure that the room is well-lit. The KIT uses radar to track data, and it is important that there is enough light for the radar to function properly.
Third, you will need to make sure that the room is free of obstructions. The KIT uses a 360-degree field of view, so it is important that there are no objects in the way that could interfere with the tracking data.
If you keep these things in mind, you should be able to use the Full Swing KIT indoors without any problems.