It ether works or it doesn't.
When it works, it's great, it almost doubles the frame rate and i never noticed any so called "microstuttering"
But when it doesn't work it's super bad, low frame rates are best case scenario, often it ends up with hard crashes.
Overall if say it's worth it since i managed to get the MSI card for 30$ used.
Most games that are demanding already support SLI and those that don't, they work well on single gpu anyways.
Only Wolfenstein New Colossus being the exception so far.
Switched to AMD 2 years ago and never looked back. If not for 1440p monitor I could still run pretty much every game at max. Looking forward to RX Vega now but I don't see the reason to upgrade since my gpu still runs good.