I don't know about this, but does BL kit guarantee an ecto?
BL kits have a 50% rare rate, master and mystic have a 25% rare rate. Neither guarantees an ecto.
If you're just salvaging the rares to save up ectos for your own use, by all means use whichever you have. BL kit will give you double the ectos in the long run.
But ... if you're salvaging those rares with the intent to sell the ectos, you will lose money (compared to just selling the rares on the TP) unless you're using Black Lion salvage kits.
Of course, if you're buying gems with gold to get the BL kits, you're probably losing even more gold. I'm not doing the math for that lol. BL kits are a once in awhile bonus for me to make a quick few gold, if I happen to get a mystic key and open a lucky chest.