OK so as I have successfully added two new keys to join my only remaining intelligent/Smart key I thought it would be the nice thing to let folks know how and a bit about the tool and experience.
I bought two OEM keys 285E3-7W00D from Amayama and these came in nice Nissan boxes with all the OEM tags etc, made in Japan. I tried to use the manual method to pair them but the car would not go into the programming mode.
I then looked at all the options online for different tools and landed on a $179.99 eBay special of the ThinkDiag2 tool from OBD_Tools. This was a gamble because its website was not listing the car at all on their site. Also because the other OBD2 sellers with much more expensive tools said they couldn't do it, didn't have a tool to suit etc. etc. I actually tried to cancel the eBay sale because I thought it was not going to work.
So I got the tool today and just gave it a go, and it worked! Paired both Smart/Intelligent OEM fobs/keys. And yes with just one of the new keys I can start/drive the car, and the immobiliser functions properly.
My car is a 2006 PNM35 Series 2.5 AWD VQ35DE so ymmv if you have something else.
The tool does erase! your existing keys and it does it at the start and frankly, the app (iPhone ThinkDiag+) is short on UI design, some work needed there, it just erases them at the start of the process and without a warning at that step.
So it will erase your intelligent/Smart keys and when I did it, thinking I had stuffed up by doing this, I stopped trying to add keys and left the car, even though the app said it had registered the first new key, the buttons didn't work until I turned off the car and closed the doors. Then I momentarily clicked the lock on a new key and it worked.
The car ignition does need to be in the ON position, OBD scanner attached and the App and scanner do prompt to tell you this. Some of the App prompts and critical stages in the app are quite good, in that they ensure your car is in the right state to proceed to doing scans or programming.
Initially I scanned the car before doing anything with the Smart key function and it did identify the protocol used by the car so I was at least confident it would have some connectivity.
Interestingly, it has this PIN code function that I have seen on the expensive key reading decoding tools ($1k+), and the Diag2 was able to pull the Encrypted PIN (Pre-Pin) and tell me what the PIN (5 digit) and 4 digit passwords (old <2010 and new > 2010) were as well, which if its correct is very impressive (mostly because F the expensive machines and paywalls).
So PM me if you have any questions, noting I have only just got this key add done and done a quick scan for any DTC codes (none were showing on the dash, none showing on the scanner).
DYOR and YMMV but I think its an OK tool if it saves me dealing with local Nissan dealer for an import. Note the tool has a 12 month software sub but after that, you have to pay them for the next year. This makes sense to me as it would be how they ensure they can offer a tool with good software in an affordable price range.