Fids have limited use, the Selma ones are better than Samsons if you do get some. I’ve rarely used a pusher, it came with the set I got, but wouldn’t buy it separately. Bent piano wire is a better option. Hand sewing needle from a hobby Lobby are better than the sail maker needles, which have sharp points that cut fibers as the go through, generally sold with splicing supplies. There are also splicing needles, but are very thin and most people break them.
You can usually judge how successful your splice is by looking, smooth, even taper, no lumps or bumps. If wanting to test, Arbsession is fairly cheap and usually fast return.