When I bought my flash last Christmas, I went for one of the cheapest options and decided to buy the EF 530 DG ST for my Samsung/Pentax SLR. It was a lot cheaper than Pentax models or Sigma's top end EF 530 DG Super and I thought I would not really need the wireless option anyway.
Since, I discovered that I was probably loosing some possibilities to have fun and that I could not even try the tricks from Strobist blog for example.
A simple cable is hard to find and amazingly expensive... something around 150€ !!!!
Then I spotted the Cactus flash triggers but they are indicated for "EF-530 DG ST (for Nikon only)". Browsing the web shows loads of problems with the EF-530 DG ST indeed.
While wondering what I could do, I noticed someone's comment (can't remember who/where but I thank you Mister!) saying that the best to do was to try the flash on a old "dumb" camera... if it fires, it is compatible!
I tried my flash Sigma Flash for Pentax on a quite ancient camera and it worked fine so hope was back.
While listening Déclencheur's chronicle, I decided to buy a cheap "Flash Remote Controller" from an Asian Ebay shop.
I went for the Seagull SYK-3 at cost of US $6.49 inc. postage and I am happy to report that it is perfectly compatible with the EF 530 DG ST for Pentax.
I am ready to bet this is also the case for Cactus's models (and its clones) so basically it seems that there are 2 categories of "EF 530 DG ST" : The Canon (and Sony) version on one side in need of very specifics signals on their pins, and the other side, the Nikon & Pentax version which is happy to fire when triggered crudely.