I'm an ex American Spirit Non-Filter smoker. I'd say the best and easiest concentrate to use is Capella's Sweet Tangerine.
If someone who smoked cigarettes that have more nicotine, tar, and flavor than many cigars suggesting a fruit flavoring sounds odd, well, I'm odd.
And the last I knew, MFS used Flavour Art flavorings and FA tobaccos are tricky buggers for a new mixer to use. That's what I started with. Took me 5 months of playing with them to make my first great
tobacco mix.
Capella's Sweet Tangerine is 15% of flavoring with your nic and PG/VG to your desire. Quick, easy, tasty, and gives you something to vape while working with FA tobaccos to come up with something that won't peel the insides of your eyelids out. And, yes, that 5 months involved
vaping quite a volume of crap before I even got close...