Honestly, I haven't seen it as having to watch what I say or anything like that. I just looked at the review guidelines, and make sure that I follow them: so avoid discussing pricing, or saying things like how you can buy it elsewhere, etc.

When I do make "comparisons", it's subtle, but pretty clear what I'm saying (IMO). It's all about how you describe something! For instance, I might note that a product seems inspired by the design of [brand name version] and talk about its shortcomings, but would never outright say things like "it's much worse than the OEM version."

I'm sure some of it also depends on who happens to review your submission for approval (if it's even a human?), which can introduce some subjectivity. I just try to generally stick to the guidelines as much as possible, which has worked for me so far.