Using the search in the subreddit lets you see what the price is usually on sale at, and around what time of year. Sometimes the current sale isn’t worth buying. People would comment in the threads mentioning that.

You can also read everyone’s comments on that specific product in either the current thread or the old ones to see if it’s worth buying or not for yourself.

Do note that a lot of these have 30-100 comments that are helpful for users to read.