Suggest you look into buying 100mg/mL nicotine liquid (most select 100%PG base for easy dispensing).
A few possible reasons:
You can always dilute the nic but it can be a little more difficult trying to boost the nic accurately.
Cost per ml.
Never have to worry about having the right nic strength.
Cleaner to keep track of with respect to buying bottles of different strengths, if you decide to change.
Where to
buy? Suggest trying the ECF search function in upper right hand corner (google/Youtube may have an answer) of this post. Could type in "best nicotine".