The Hero5 Session is almost identical to the Hero 5 in specs, except in a smaller and more compact form – which may be a big plus if size matters to you. The Session only offers a 10MP camera (instead of a 12MP on the Hero 5), but like it's big brother, handles up to 4K video. Other than camera resolution, what you're sacrificing for a more compact size is a touch display, location capture, and ability to capture RAW + WDR Photos.
Read my article: Best (And Cheaper) GoPro Camera Alternatives for your Travel Action Camera Needs.