The NGC tag will be important in the future. NGC has photographed the coin, and with the tag you get the photograph https://www.ngccoin.com/certlookup/4251253-001/ which may not be important to the advanced collector but some people will appreciate. If Roman coins ever come under some kind of heritage law where provenance becomes necessary to sell the coin, as recently happened in Germany, NGC has records of when the coin was encapsulated. Encapsulation date isn't currently available on NGC's "verify" web page, but it could be added, and then the ID will be a nice proof that the coin was on the market in 2016.
You don't need that chisel. Just stand the slab, on its short edge, on a concrete floor. Tap the opposite short edge around a corner with a heavy hammer. I use a short handle sledge with just a little force. It cracks the slabs at the seams. Start with a small force and increase slightly until it cracks open. Then just spread the slab apart. They will open like a book. If not, repeat the procedure on the other corner. It's a non-scary procedure. Attached are some results.