MacDev is simply the ****.
I have a 45/45 conquest(made by macdev), and a gladiator(also made by macdev
).
I haven't used or known anyone that has used the yingyang bolt, but I'm sure it can't be that bad.
I would however suggest you buy an 'AKA Lightning-Bolt' cocker bolt. I have used a few of these in past cockers, and they are the best bolt I have ever used.