If you have a 30a breaker and at least 10 gauge wire you should be good for a 24a EVSE, no need to limit to a 16a EVSE. I'd get at least a 20a EVSE but better yet a 24a and use something like a L14-30 outlet which is nice and heavy duty.
Note you could just purchase a 24a EVSE but personally I'd look for a 30a model that can be de-rated for 24a, that way if you ever get a 40a circuit you can charge the max your Leaf can pull(27.5a or 6.6kwh).
Since your car has the 6.6kwh charger 27.5a is the max it can draw, if your EVSE is less it will only pull that whatever the max of the EVSE is, if you plug a 30a fixed EVSE into a 20a circuit it will try and draw 27.5a and quickly blow your breaker, IOW the car doesn't know you've plugged the 30a EVSE into an underpowered circuit but if your EVSE lets you dial down the amps it will only draw what you've set the EVSE for.
Juicebox makes some adjustable EVSEs as do other mfgs. Some just use jumpers, some adjust the amperage otherways and the modern Juiceboxes use a cell phone and internet connection to adjust the amps.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a