There are a few things to consider when purchasing a kayak pump. The first is whether you need an electric or manual pump. Electric pumps are great for inflating kayaks quickly, but they can be more expensive and require a power source. Manual pumps are less expensive and don't require a power source, but they can take longer to inflate a kayak.
The second thing to consider is the size of the pump. You'll need to make sure the pump you purchase is the right size for your kayak. If it's too small, it won't be able to inflate the kayak properly. If it's too large, it will be more difficult to use.
The third thing to consider is the type of valve on the kayak. Some kayaks have a Boston valve, while others have an inflation valve. Make sure the pump you purchase is compatible with the valve on your kayak.
The fourth thing to consider is the price