You rarely get any problems with sparklers IME. They are quite peaceful. Even when they breed, males will threaten each other but rarely get into actual scraps. As for males attacking females, this is rare. It's quite common in some of the larger gourami species but, with sparklers, as long as there aren't more males than females, you should have absolutely no problems.
I think in another thread you also asked about honey gourami aggression during breeding so I thought I'd mention that here. These are more like what Miss Dib Dabs described as you'll get the occasional torn fin. Still, they won't usualy cause serious injuries to each other. Males may fight but preffer to simply display and flare. Females will get stressed and chased if they do not out-number the males. It's best to keep 2 females per male.
The gouramies that usualy cause most harm to each other are the three-spots; with pearls probably being the most gentle.