I have not tried doublers yet but it makes sense especially if flavor is a big deal to you,
(somedays i just don't care/taste much)
... I diy my base (18mg) from 100mg vg ...
& have learned that it is easy to adjust 18mg down a little with flavoring & extras...
so I end out with something in the 14.5mg-15mg range ...
...when I order pre-made flavored juice's I always order
18 mg w/double flavor (if available) & add a little vg to it to get to the lower nic level *...
my favorite for example is 8ml 18mg + 2ml vg = 10ml 15mg*
I like the whole # route better than all the 1.4ml type measuring ,not very scientific or precise, but works for me
Play with the juice calculator for awhile & you'll figure out what works for you .......
*approx.probably a little lower, which is ok & does not change flavor much
ooops did not mean to hyjack post , in answer to 1st ? the
diy forums are wealth of knowledge & look in to joining the
PIF group , as you collect more stuff... that is a great place to trade stuff & try new stuff.