You can use a neutral cream on a clean cloth and this will not affect the waterproof qualities of the shoe. Both a neutral cream and a neutral polish are useable. However, as this is a casual style, a cream is preferable as it will maintain the characteristic of the leather. A polish will, over time, make the leather a little glossier / dressy in appearance which will change the look of the shoe.
You could also use a colour polish, but the shoe has got contrasting stitching, which would gradually turn the colour of the stitching and you will probably find it difficult to buy a polish to match the colour of the shoe/boots.
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