Nice combo, I like throwing the headbutt into it. That would really help set the throw up nicely. I also like how Boyd stays on top for the armbar instead of giving up position and falling to his butt/ back for it.
That is a favorite entry for many JKDC guys, particularly Paul Vunak. If anybody knows Paul, he can headbutt like most guys throw a good jab. If you watch Paul's Dumog video, he demo's this exact entry minus the takedown very similarly. The only difference is that Paul would follow the headbutt with a panajakman knee kick to the sciatic nerve and a horizontal elbow as well. A high-low-high strategy of hits.
There are numerous follow ups for this entry. That is why I like it so much. I like any entry that puts you to the side of your opponent. I mean, why stand in front of him where he can use all his weapons against you? I like headbutts a lot, because they are effective no matter what your size or strength. I think many throws are functional because the ground is the biggest weapon in the world and often the hardest. Sombo stresses throws with control. This training allows for effective follow ups without giveing up your personal safety in the process.