Well, i wont say ''Instantly'' but it might be, maybe youre flagged, maybe not, i have a switch with 90dns and still not banned since almost 1 year, but you must have in mind that it will come someday, i would say it is 99.99% safe.Is it instantly bannable, or will 90 DNS prevent me from getting banned and allow the online features to be used indefinitely?
This is the EmuNAND I use for hackery, with multiple NSPs installed. My only emuNAND, actually.
As long as 90DNS is installed to your emuNAND, you will not be banned for anything you do with your emuNAND. However, you are unable to use Nintendo services like online play and the eShop with 90DNS installed.
You might want to consider using Incognito in addition to 90DNS. That way, if something stupid happens (loan your Switch to a friend and they connect it to a different Wifi network, connect to a Wifi network and forget to setup 90DNS, Nintendo releases an update that uses hardcoded static IPs to reach Nintendo servers, etc.) you won't have to worry about getting banned.