Although Noctua refers to the mounting system on the NH-L9i as their SecuFirm2 mounting system, it's actually quite a bit different than the SecuFirm2 system I'm used to seeing on their coolers. All the larger format Noctua coolers that I've reviewed have used a two stage mounting system; a mounting bracket and backplate is installed on the front and back of the motherboard, and then the cooler itself is screwed onto the bracket system. The NH-L9i has collapsed that design into a single step system where you simply hold the cooler on the front of the board and attach is using four thumbscrews from the rear of the board. The AMD variant does have a backplate included, but still uses the same four screw design.
With the cooler flipped over you can see the steel brackets on the cooler which the four screws attach to. The base of the cooler has a similar design to most Noctua coolers I've used; that is, it's not lapped perfectly smooth and does have some fine ridges in it.
There's a couple compatibility points worth mentioning about the NH-L9i too. First, the cooler's size is such that it won't interfere with the memory keep-out area defined by Intel for the 115x socket type. This means that the cooler won't cause incompatibility issues with chipset coolers or RAM modules and RAM heatsinks. Also, the NH-L9i is designed so that it won't interfere with devices in PCIe slots that may be closer to the CPU socket on some mATX and ITX board designs.