Lots of good suggestions so far. You definitely have room to add a redundant system in there. What you have will probably work just fine. This looks far better than any of my first attempts to build one. My comments below are really nit-picky things that I'd suggest, but not necessary.
1. Restrain power wires much better, particularly where they feed into the screw switch. I'm assuming you are using braided wire, annd the solder can wick into the strands and make it brittle. There is little strain relieve there. I cannot see how the power lines enter the PCB as it's from the back of the board. Just make sure you also have strain relief there as well.
2. Add a 3d printed cover to the switch to prevent the screw from coming all the way out when you unscrew it. This allows for positive feedback when turning off, will restrain the screw when you back it, preventing vibration when traveling from making intermittent contact, etc. There is little more frustrating than turning the screw too far, having it fall out, and then needing to open up the alt bay, have the screw fall on the cold, snowy ground, and lose it. Not speaking from experience or anything. You can buy them from MissileWorks, make your own, or I think I even have some up on Thingiverse somewhere. My guess is you would not have to change anything other than adding this as you have plenty of room.
3. Those audio connectors will get brittle over time. The plastic isn't really meant to hold up to the elements and ejection charges. They will work for a while, but treat them as consumables and replace every 5-10 launches or so. You can extend their life by covering with a vinyl cap.
4. Not thrilled with the routing of the power lines under the ISM band radio antenna. Probably not an issue, but near field coupling from antenna to power lines isn't a great idea. The regulator and decoupling should take care of any coupling, but I'd probably route the power lines differently where they are not in that close of proximity.
5. As lots of people have mentioned, having a monopole antenna parallel and close to the all-threads will hinder performance. There is a lot of margin though, so probably ok. When in doubt, it's always better to slide as far from the all-threads as possible.
Ground range testing is a great idea. However, don't get discouraged with the results. That system does not give great range with both the tracker and the ground station on the ground. However, it does give good range when the rocket is about 100 ft and higher. Treat your ground range testing as a relative performance metric. I know that makes it hard to quantify as you probably don't have other trackers with known performance.
My only worry is that the amount of metal may affect your tracker signals, but it's probably unlikely. Eggtimer is one of my favorite brands, as long as your charges are sized, you should be fine.
