For a wild action film, First Option features unusually accurate tactics and weapons-handling. This is likely due to the real-life SDU members consulting on the picture. Also, unlike John Woo and his other famous Hong Kong contemporaries, director Gordon Chan has always leaned towards authenticity in his action scenes. You can see the pinnacle of this approach in "2000 AD", a more recent Chan film that features stunning shootouts. But First Option is certainly an action-packed film as well. Definitely a must-see for fans of military/specops movies.
One note about the casual wear outfits: They are realistic. If you ever bother to research beyond glossy promotional photos, you'll see that real military and SWAT units can and do often wear civilian clothing during operations. Whatever works best for the situation. That's the whole point of these unconventional units! In this case, they're operating in a tropical, urban environment. Jeans & t-shirt are comfortable, sturdy, inconspicuous and a lot more appropriate in the heat than full hooded flame resistant jumpsuits. And they are not missing any of their important gear (assault vests, pouches, holsters, weapons, etc). It's funny that when a film tries to be LESS flashy and movielike that it gets accused for being unrealistic!
As for the SEALs being beaten in the film, I disagree that they were beaten "easily". In fact, they defeat the SDU at one point and there's a scene where the SDU discuss the fearsome reputation of the SEALs. When the SDU finally triumph, it's far from "easy". But last I checked, no training in the world makes men bulletproof. Just because the SEALs have a superhuman reputation, you shouldn't start believing that only kryptonite can bring them down. The ultimate triumph of the SDU is quite reasonable given the way the scenarios are set up in this film.