I've watched/helped friends do various types of finaplix conversions before. One guy just crushed the tabs up (used a single cartridge of 2g fina), mixed it with a little bit of BA and added enough oil to make it in a 50mg/mL concentration. Then he heated the mix for 30 minutes and didn't bother to do anything else. He used the entire vial of that shit and now he can't inject into his quads anymore b/c of the scar tissue the injections and the binders probably cuased (he used only his quads for the fina and his glutes for the test he ran). His reason for not filtering/using a kit was b/c he claimed the binders weren't harmful and the filtering would take out too much of the fina.
Another guy made him and I some really good stuff from tren carts. He was able to get the pure finaplix crystals and the results looked great and were very pure, etc.
Whatever you do, take your time and be safe. I actually just buy pre-made tren ace b/c I don't save much by making homebrew fina . It would cost 60 dollars for me to make 2,000mg of fina or 20mL @100mg/mL whereas I can buy TWO 10mL 100mg/mL tren vials for 90 bucks. So the savings are minimal and the stuff I buy is painless. But if you want a quasi-legal method then by all means go with the kits and cartridges.