I used to use a barrel bolt approach for a bolt-on neck. However, I had two 'incidents' where the neck heel cracked. One was a severe shipping issue, and one was a ukulele on a stand that got kicked over on-stage and did a header. Kind of extreme cases, but they pointed to a weak point since the breakage was the same in both cases.
The issue is that with the barrel bolt one must drill out a hole in the neck heel for the barrel bolt, and then a cross-hole for the neck bolt. The neck heel has the grain running across the heel, so with the removal of the wood for the barrel bolt there is not really much wood left, and the grain is perfect for a crack/split. The issue is illustrated in the first picture.
I have since gone to gluing an oak cross dowel into the neck, and then using a brass threaded insert. I use "E-Z Lok 400-4 Threaded Insert, Brass, Knife Thread, 1/4"-20 Internal Threads, 0.500"" because they have really sharp wood threads. The dowel has a larger diameter than the threaded insert, which means that:
1) The threads of the threaded insert are biting into cross fibers of the oak dowel, not end grain as would be the case if the insert was threaded directly into the end of the neck. Much stronger.
2) Since the insert is a smaller diameter than the oak dowel there are oak dowel fibers that run all the way up and down the heel, meaning that it is very difficult to crack horizontally.
3) There are no voids in the neck heel, solid wood.
This is illustrated in the second picture.
As a test I built a test neck with this setup, bolted it to a block, and then dropped a 3 pound sledge hammer onto the outer end of the 'neck'. It just bounced, the neck was fine.