I knew I used the wrong term for the serger stitch. You are correct: every serger can do overlocking. However, the t-shirt hem stitch is called a cover stitch, and very few sergers can do that.
You can mimic it with a regular sewing machine and a twin needle, or by using a blind-hem foot for overlocking, or you can buy an expensive “cover stitch” capable machine.
Dressew carries stitch rippers. I haven’t had any problem with the ones I’ve bought there. I have one that has a longer flat handle instead of a small round one, but I can’t remember if I bought it at Dressew or somewhere else.
Lee Valley Tools also carries a “Pro Seam-Ripper kit” with a few different blades. I’ve bought the kit, but haven’t used it too often, so can’t tell you if it is much better or not. I can’t even remember where it is right now!