Here's my take and
only mine on this topic. I am not a professional making my living off of photography. There is no income paying for my equipment and I don't have unlimited funds to purchase equipment. Therefore, I prioritize and research all my photographic purchases to obtain the best equipment within a budget to do what I want to do. When I look at flashes and see a third party that admittedly has been reverse engineered, not necessarily a bad thing, to match all the capabilities of the OEM at a price considerably less, then I have to seriously consider that purchase. When I compare the Sigma EF 530 DG Super to the Pentax AF-540, it meets or exceeds the OEM in functions at a price $196 cheaper, I'm sorry I have to go with the Sigma. Its not like Sigma is a fly-by-night company. They just happen to be the largest maker of third party photography equipment in the world. When I had a problem with one of my lenses in an emergency situation, they paid for the shipping on a Monday and I received the repaired lens back on Thursday. That is a total turnaround of four days! That was impressive. If I was a pro and funding, even the ability to write if off on my taxes would help, was not an issue, sure I may go OEM, but sadly that is not the case. So for me its whatever will get the job done in my situation at the cheapest expense. This may be heresy to some, but oh well.
Everyone have a great photography day.