Jig kits can be hit or miss a lot of the time. There can be instances when the dimensions are off, or the price just doesn’t fit what you are willing to spend. Maybe you messed one up and now you can’t build the 5 other lowers you wanted to get done by the weekend. Jig kits can have their problems, especially when different generations come out that fix other problems the previous gen had. Some can only be used by drill presses and so forth.
That is why I like the Anderson mfg AR-15 jig gen 2. It tackles the problems of the previous gen and comes with the drill bits you need to finish the lowers as well. I have bought around 3 jigs from them from the gen 1 and the gen 2 and I can ultimately attest to the clear advantages that the gen 2 jig has over the gen 1. The jig kit comes with instructions on how to build them and from what depths to start your milling.
Anderson really improved on the gen 1 and when it comes to building consistently I trust the precision of the gen 2 jig. It is harder to get drill bits to the measurements of the holes you need, so I really like that the jig kits come with the drill bits. I know of some places that only sell the jig and then it makes it more expensive when you go to 5D Tactical just to pick up some drill bits. For these reasons, I highly recommend Anderson mfgs gen 2 jig kit and drill bits for the AR-15.