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Decoart Easy float and Delta Colour Float are all drying retarders, but the Jo Sonja takes much longer to dry than the others and it's overall properties are quite different. Americana's easy float dries comparatively quickly. Now the artist may choose the Jo Sonja one because it takes longer to dry...it may be very specific to the work. Read the instructions of a pattern before you go substituting...see if the alternative product you have might do the same job. Test it on a scrap piece of wood first.
The other concern is that while products within one painting system are compatible with each other they are not always compatible with other brands of paint. You will find different levels of success if you use say one brand of cracking medium with a different brand of acrylic paint. So again...try to stick with what is called for, or change the complete project paint list to another brand of paint.