Kapow offers a wide range of strengths within all their e-liquid lines. Kapow will of course offer a nicotine-free option for almost every flavor they produce. This is common in general with all e-liquid brands. It is a rare thing to see a brand that does not produce a nicotine-free option.
All e-liquid bottles and brands in Canada, Kapow offers two varying sizes of e-liquid bottles. There is a 60mL size and a 30mL size. The 60mL size bottles will always and only contain freebase nicotine at strengths ranging from 0mg, 3mg, 6mg, and sometimes 12mg. The 30mL size bottles will always and only be salt nicotine with available strengths at 10mg and 20mg nicotine. The stronger strengths are in smaller bottles since there is a higher concentration of nicotine in them. The same goes for the 60mL bottles. Since they contain much lower concentrations of nicotine, a larger amount can be sold in a 60mL bottle.
It is generally safe to use any kind of liquid from any brand as long as you have the correct setup for that nicotine level. There is also the issue of determining whether you want to be using salt nicotine or freebase nicotine. Most kits like many from Vaporesso, offer two various pods or coils with different resistances. The coils or pods with lower resistances are best used with freebase Kapow e-liquid. If you are wanting to take in a much stronger dose of nicotine, it is better to use the higher resistance coils or pods, with salt nicotine.