It's easy to get sucked into specs, but more isn't always better for your specific needs.
Magnification: Most hunting rangefinders offer 6x or 7x magnification. This is perfectly sufficient for most big-game hunting scenarios. It provides a clear, stable image that makes it easier to hold the rangefinder steady on your target. Higher magnification can make the image shakier without a tripod.
Maximum Range: Ignore the extreme maximum range figures (e.g., 2000+ yards). These are for ideal conditions on highly reflective objects. Instead, focus on the effective hunting range. A good rule of thumb is to choose a model whose maximum rated range is at least double the distance you plan to shoot. If you take shots out to 400 yards, get a rangefinder rated for 800+ yards. This ensures it can easily and quickly range a deer-sized animal (a low-contrast target) at your maximum effective distance, even in low light.