Hi Joshua, and welcome to WoodworkingTalk! By now, I think you have figured out that this is one of those decisions that only you can make, and whatever you decide will be right for you.
You must find your own path to satisfaction in woodworking. Only you know you, and your interests will evolve over time.
* No delay before it is ready to use (after assembly, safety training, and practice).
* Manufactured device may have more features, easier to use, more accurate, etc.
* Manufactured device may be made of more durable materials, such as metal or plastic, that are less sensitive to temperature and moisture.
* Assumed to be accurate (or easily calibrated) out of the box.
* Lets you focus more on the project and less on the jigs you need to make it.
* Limited to what is available on the market, which may not match your needs perfectly.
* Usually costs more than making it yourself.
* Usually lower cost.
* Custom designed to your specs. You can add features or build it to the exact size you want.
... or dumbed down enough so that you can build it. :-)
* No guarantee you'll get it right. What if you have trouble squaring the fence on your homemade sled?
* Guaranteed you will get some woodworking education - skills, knowledge, and experience.
* Takes extra time away from projects. Whether that is a problem is a matter of opinion. Jigs are fun - you can make them from scrap and you don't necessarily worry about the finish.
If you have the time, I think you should build the sled for the following reasons:
* More forgiving. If you drill a hole in the wrong place on a sled, nobody cares. If you drill a hole in the wrong place on a small jewelry box, it might ruin the piece.
* Gaining a quality woodworking experience of the best kind. The more you learn, the faster and better you will be. I know woodworkers who can grab some pieces of scrap and assemble a needed jig faster than they can drive to the woodworking store to buy it ... and it will cost them less than the fuel to drive to the store.
At our local woodworking club meeting last week, the speaker was demonstrating various kinds of joints for boxes and drawers. He kept showing small handmade jigs, squares, etc., saying, "You can buy something out of metal or plastic at the woodworking store, but I prefer to make this instead." I liked his jigs and squares. Nice stuff.
For me, I want to build more, but I get lazy and buy it. Those old guys seem to have had more time for jig building. :-(