Is it better to use the theme or come up with your own idea because it says in the description that the theme is intended for guidance
I feel like there is no better or worse option here. Some people will probably feel like the theme is perfect and can come up with an idea but if some doesn't like the theme or they don't have an idea for it and/or they just wanna make a different game other than the theme then they are more than welcome to do so. So it's perfect for everyone and there is no pressure on using the theme.
its all up to you
i love using the theme because its hard for me to think of a game idea, but its absolutely your choice
like @armin.remenyi said there is no bad/good its only up to you