Depends on what year EVSE it is. Newer ones can only be upgraded to 16a, of course, if you only have a 3.6kw Leaf charger that would be OK, otherwise, if you have the 6.6kw charger, you'll only be charging ~1/2 the speed you could. Nothing inherently wrong with using a EVSEupgrade permanently though, if you're OK with possible slower charging than max.
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