Hi Andy,
My primary requirement for garden boots is a smooth sole that will not track in mud or soil into the house. Traction is not an issue in my garden, so those soles that are designed for traction just accumulate soil or mud in their crevices.
Another primary requirement is also that they fit. I have wide feet, and finding boots that are extra wide can be a problem. I spent over an hour in a local boot store without finding a single pair that were wide enough in my size. My feet have widened and apparently lengthened over the years, and my shoe and boot size is now 11EEEE or 11-5E depending on the manufacturer. Many (most) boot manufacturers do not make boots that wide. I am currently wearing some 10.5-5E Propet snow boots that happen to fit OK as long as I don't try to wear extra-thick socks. They would not serve as garden boots because they have snow-tire like treads to be non-slip on slippery conditions. And they have too much insulation for most garden work. My current garden boots are several years old and their soles were coming unglued, so I had a shoe repair place re-glue their soles. I will probably purchase a new pair in the 11-5E size with smooth soles to start the gardening season this year.
I now purchase my boots from Amazon, simply because Amazon is the only place that is handy for me with the extra wide widths that I need. Amazon has a workable return policy with boots (you do have to save and use the original packaging), and I used Amazon's return procedure earlier this year to return a pair of 10-4E boots that I had purchased. I have a pair of New Balance shoes in that same size that still fit fine, but apparently they have stretched some over the years, and that pair of boots in that size felt tight. So I returned them and purchased the pair of 10.5-5E Propet snow boots that I am now wearing. But I now consider 11-5E to be my "new" boot size, and recently purchased an every day pair in that size, and I like their fit. So I will purchase my garden boots in that size.
ZM (not associated with any product or vendor mentioned or linked)