It's crap at the moment (GT-BE98).
From my testing, I have both MLO compatible devices and legacy devices droppoing to use 2.4GHz only, and there's no latency improvement (at a non-congested location) with very little performance difference.
One of the limitations is that you can't separate each band after enabling MLO (although if you were using smart connect before, this makes no difference to you). I still don't know why they don't leave all bands separated for those who need it and create a new separate SSID for MLO.
Hopefully ASUS will release another firmware update for the BE98 next week.