I don't use either product -
But it would seem to make sense to me to use the products as directed, if one is going to go to the expense and effort of using them.
I soak new fabrics (similar colors and/or shades together) in water as hot as it comes from the tap (not hot enough to scald myself if I do a quick dip in it - but quite uncomfortable if I linger in it) for at least half an hour.
I use the sink if I have a lot of items, a small kettle or bowl if it's something like a fat quarter.
I smoosh the fabric(s) up and down a few times in the water maybe every ten minutes or so just to stir it up a bit.
If the water is still clear, all is good and I put the piece aside to be very gently washed and dried.
I think the agitation is what makes new fabric look "worn" in the washing process.
If the water has acquired some color - I go through the pieces and see which one is putting out the color.
I isolate that one and soak and rinse it some more until the water is clear - or almost clear.
Then - when I think that the black (or whatever color) piece won't discolor that white (or other lighter colored) piece - I dump all the wet stuff into the washer and give it a quick gentle wash with just a smidgen of detergent - dry it on permanent press in the dryer until just dry - fold and put away until time to cut it.
If I get a piece that continues to color the water - I will try to return it (if it's a relatively recent purchase and I still have the receipt)
If the store won't accept it, I discard it. No point in mucking up my project or someone else's.
I've had a couple of pieces that were still coloring 20 changes of water. There comes a time to accept that the piece is a loser!
The stuff I make goes to people that do well to get things washed - forget about "special treatment"
I do have a hissy about using liquid bleach when washing quilts.
I have this idea that fabric should behave "on its own" and that the owner of the quilt should only need to use "reasonable care" when washing it.
I do know about color catchers, etc. I just don't they should be necessary!