The ResQLink 410 is an older discontinued model while the 425 is the newer, upgraded version. Key differences include: 410 uses alkaline batteries instead of rechargeable lithium-ion, 410 is slightly larger and heavier. 425 adds more memory, GPS compass, extra strobe modes, 425 uses latest electronic components. For most users, the 425 is the better choice over the outdated 410 model.