What you made before was not what I'd consider biodiesel but rather a just a variant of SVO (straight vegetable oil). The kit you are talking about uses reactants with the UVO (used veg oil) & the end product is biodiesel.
If you have a good, cheap supply of lye, methanol, UVO & TIME, it's a no-brained to run biodiesel... Even if you don't run B100, you can still saves lot of money over time.
Do you have a secure supply of UVO? You'll get about 1 gal of biodiesel for every 1.2-1.5 gal of UVO iirc. The systems I've seen made 20 gal batches using 25 gal of UVO & about 2-5 gal of methanol & iirc.
Look up "Appleseed biodiesel". It's a homebrew kit using an old/new hot water heater rather than the nicely setup/automated, expensive kits if you want to get into it cheaply just see if it's going to be lucretive for you. And if so, you can splurge on the nice automated kits.