The DA+ action is kinda quirky and gets a lot of raised eyebrows and chuckles at the range, but is really just extra linkage for little extra benefit.
Not much in the way of extra linkage, but there are a few extra tiny part in the hammer mechanism -- which it is not recommended that users mess with. That "extra" stuff does not affect the trigger pull in DA or SA mode.
I've had several Daewoo DP-51s, and now have a Lionheart LH9. Fine guns. I always thought they seemed like an odd mix of S&W Third Gen and SIG, in how they look and shoot. Very solid, well finished guns that tend to be pretty reliable and accurate. You can use S&W 59-series mags (including some of the extra large capacity 5906 mags that hold 20 rounds, etc. -- but that make for a big, awkward , heavy combo. (My first DP-51 was one of the most accurate 9mms I've ever owned, but someone made me an offer I couldn't refuse. In retrospect I'd like to have it back. The Lionheart LH9 is a fine shooting gun. I wish there were more after-market parts, but with low volume guns that just isn't going to happen.
The gun's "action" has three carry/starting modes: 1) standard double action. 2) standard cocked and locked, and 3) cocked with the hammer pushed forward by the shooter. I looks like cocked and locked, but is really more like DA with a much lighter trigger pull.
The safety can be used in any of these modes but some consider it unnecessary in modes 1 and 3. Once fired, it's standard SA like most DA/SA guns..
In Mode 3, the trigger acts like a two stage trigger -- with the initial pull flipping the hammer back -- you then continue the trigger pull, if you choose to, which releases the hammer/sear just like with any DA/SA gun in SA mode. With all of mine, that stage (a bit like a minor hitch) is very pronounced and it's easy to NOT pull through if you don't mean to. (I also had a DH-40, the 40 S&W version of the DP-51; at that point in my shooting life, I was unhappy with .40 -- I've since found more comfort with the caliber.)