Option 1: goes in the small tank
If it lives, you're fine.
if it dies because it doesn't eat, you're sad your new wrasse died
if it dies because it's sick, you're sad your new wrasse died
Option 2: goes in the display
If it lives, you're fine.
if it dies because it doesn't eat, you're sad your new wrasse died
if it dies because it's sick, all of your fish die and you have to make your display go fallow for months
If you bought it QT'ed, the variables change. Odds it might die from stress or not eating could be different in the small tank vs main, but not clearly either way. However even if the odds were higher in the main tank, you're trading the odds of that one fish being better versus a big PITA for everything else.