The Noctua NH-L9i is a very well-made, low-profile CPU cooler, with the same construction quality we are accustomed to seeing in other coolers from this manufacturer.
However, there is no point in comparing the cooling performance of such a low-profile cooler to the high-end tower coolers. Therefore, we must pay attention to the data comparing the portrayed cooler to the stock cooler and other low-profile models.
The NH-L9i is shorter than the Xigmatek Praeton, the Phanteks PH-TC90LS, and the stock cooler. It performed better than the stock cooler, had a performance equivalent to the PH-TC90LS’s, but presented worse performance than the Praeton. It was, however, quieter than those retail coolers, being almost as silent as the stock cooler.
So, if you are building a PC (or an HTPC) in an SFF case and looking for a really low-profile and quiet cooler with better performance than the stock cooler, the Noctua NH-L9i is a product to consider.