If you're considering purchasing a four wheel walker, there are a few factors to consider. The first is your age, since different models are designed for different ages. Secondly, the weight of the walker and its accessories will determine the type of terrain you can use it on. Thirdly, how often you'll use it will affect your choice. Fourthly, consider your personal fitness level. Finally, consider your budget. 

When choosing a mobility aid walker, keep in mind your age and weight. Different models are designed for different ages and weights; some can accommodate people up to 300 pounds while others are designed for those up to 500 pounds or less.

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Additionally, the type of terrain you'll be using the walker on will affect which model you should purchase. For example, an all-terrain model is best suited for rugged terrain such as hiking trails or fields; a suspension-type model is better for paved surfaces or streets; and a self-propelled model is best for short distances across lawns or indoor surfaces. Weight also affects how often you'll use the four wheel walker; those with lower weights can use them more frequently than heavier individuals because they require less effort to push forward.

Depending on your personal fitness level and budget, you may want to choose one of three types of four wheel walkers: manual operated (where users power the walker with their own muscles), electric operated (which uses batteries), or self-propelled  (which uses an engine to move the walker). 

Manual operated walkers are the most common, and are easiest for those with lower fitness levels to use. Electric operated walkers are more difficult to operate but can be used by those of any fitness level, and self-propelled models are the most difficult to use but are the most versatile, allowing users to move the walker across a variety of surfaces.