Whether for alterations or for our inevitable sewing mistakes, ripping out is an unavoidable part of sewing, so it is always nice to find a new tool or trick to make it quicker, easier and less fraught with the risk of damage. I first learned to use a razor blade to open a seam when I worked in a fabric store. Any sharp razor blade will work and, used carefully, it can be surprisingly gentle to the fabric.
While holding a plain blade carefully by its spine works pretty well, it does present a long surface to the seam, and angling it too far in one direction can result in an unintentional cut in the fabric. A handle is a nice way to get a little bit more control.
This Famore tool is not the first handle and blade I've tried. The Dritz version is worthless. Dull and awkward. An Exacto knife handle can work, but Exacto blades are so pointed at the tip that they can easily pierce the fabric (or you!). This Famore Cutlery 5.5" Seam Ripper with Replaceable Blades is the best I've found--precise, comfortable in the hand and very, very sharp. I got mine at a local quilt shop (as it was in the process of going out of business), but you can order them from the company's website.
The cutter comes with a rigid plastic cover for the tip, and it's definitely needed. This item should never be laid down with its blade exposed, as there are many scenarios for damage or injury.
Have you ever heard of Famore Cutlery or tried any of their products? Other than the cutter, I am unfamiliar with this brand. The Micro-Tip Scissors look really good, and have wonderful reviews on their website.