2 of the flavors I've got coming(tomorrow)are both from ECX...'Flavor Express' Turkish & RealCIG(on the invoice RealCIG appears as Tobacco Additive)and I'm guessing they might be re-labeled TFA flavors...And several other 'Sub' flavors...Toffee / Hazelnut etc...
I've browsed that page of "Flavors Express" flavors many times, and I've never been able to pin it down. Based on the names I highly suspect many of them are re-branded Super Concentrates, but it's definitely not a perfect selection of SC. There are holes (no Arabic, no Island, no Cubana; one of SC's best tobaccos) and then there are flavors that aren't in SC's regular line, or at least not available from my SC suppliers, like HongJinLong. I think the Flavors Express are a combination of re-brands, but heavy on SC, and I base this assumption on the products known as "Black Mile". Both TFA and SC have flavors with that name. The Flavors Express page likewise has two Black Mile flavors, a regular and a plus, and there is no Black Mile selection on their TFA (Signature) page. This is why I haven't ordered from that page. I already have almost all the SC tobaccos, and many other brands, and I don't want to end up with duplicates.
Anyway, if what you bought is SC, and it seems highly likely the Real Cig is, I can describe how I use them. For single flavor mixes, SC is actually pretty easy to work with, because their flavor line has really good uniformity in strength (they all seem to be about equal in how concentrated they are). Start at no more than 2%. I've found that most flavors are good right at 2%, but a few are better a little higher. Arabic is an exception and I've found it unpalatable at anything over 1% (soapy). From your 2%, you can adjust up or down to taste.
I don't have Real Cig or Turkish, but here are examples of % for some SC flavors I have:
Arabic: 1%
Cohiba (yum!): 3%
Cigar: 2.5%
Cubana (yum!): 3.5%
Black & Mild (aka "Black Mile): 3.5%
Island: 2%
USA Mix: 3%
RY4: 3.5%
Old Captain: 2.5%, or up to 4% if you really like Whiskey
American Red: X% (the only SC I don't like)
(Note: these are my own preferences, which may or may not differ from the prefs of other folks).
As you can see, the percentages are very tight within the 2 to 3.5 % range, which is why I feel SC is easy to work with. Not a lot of guess work involved, as with some other brands.
I have done very little combining of SC with other brands, so no comment there.
I have found that all SC flavors give a heavy metallic taste at above 4%. Even when combining different SC flavors, for me, 4% seems to be the max threshold. It seems like after sitting for a long time (months), that metallic taste will subside, but you don't end up with anything better than you would by using lower %. I haven't found the SC line to be steep-dependent, though the Arabic and Island are definitely squirly till they've had a week or so to settle down. Actually, I'd say these are better vaped within a couple months. I have old bottles of Black Mile and RY4 that have faded considerably.
This got long. Shutting up now. Good luck, please report back with your results!