It depends on the specific content, but I usually do between 2 and 4 thousand words for things like that. So about 1k goes towards explaining the topic and presenting a brief buying guide, and the rest is a list format, maybe with a pros and cons section, or something similar, that lets you use bullet points. I suggest you take a look at what your competitors are doing, I’ve also seen people put up under 1500 words for those kinds of articles, although they usually only review a few products.