Is it ok to use a 9spd link on a 10spd chain? I accidentally broke the master link (a.k.a reusable missing link) on my 10psd KNC x-10 chain.
Since I only had a SRAM 9spd replacement link, i used that to connect the chain.
I rode 30 Km without any issue, but is it a good idea to leave the 9spd link in place, or should i replace it with a dedicate 10spd link?
The problem you might run into is too much movement in the link. This will not show any problems for a while, maybe months, but the more movement there is the more damage you are causing the link and it will eventually fail.

Depending on what you are doing at the time when it fails, you might just be inconvenienced and have to walk home or, in my case when I was 18, launch yourself over the bars at 25 MPH, slide down the road and open your elbow to the bone, spend 3 hours in the ER digging out all the gravel, have a wound that smells like rotting meat, and a scar that takes up 25% of your arm 20 years later... Swap out the link when you get a chance, or better yet, buy a new chain, WAY cheaper than an ER visit!