bad in the beginning if you've never seen histological slides before. i failed my first quiz. but after the second lab you get more used to seeing real cells (rather than the cartoony drawings we're used to in undergrad) and everything is easy. the theory part is very easy- just like studying cell biology. it's not necessary to take courses beforehand imo.
This might sound utterly idiotic, but I'm being serious: histo is all about pattern recognition, right? Well, when I was younger (muuuuch younger), for whatever reason, at one point I became somewhat obsessed with finding 4-leaf clovers. I'd scan clover patches for like a half hour at a time, and ultimately I ended up finding at least 1 or 2 every time I looked. It's not about knowing where to look, but rather knowing how to look.
I've since recognized that I'm not half bad at pattern recognition, and I think I owe it in part to my youthful 4-leaf-clover hunts.
Bizarre but true.
So if I were your situation (which, as a pre-dent, I kindof am but a year behind), I'd save the money from the class and spend some time outside to develop pattern recognition skills!
Plus, once we start dental school we can kiss goodbye our free time for going outside...