Hey Scotty,
I agree with all of Dan's points... I have the screen, but like mentioned, it is bulky, and useless when head or chest mounted... It also eats battery life, so not worth the extra cash in my opinion, but nice to have to give you an idea of framing etc... They are also nice to have for playbacks etc on the boat....
You can wear a GoPro all day, they really are comfy, light and easy to forget about.
Their functions are super simple, easy to use...
I would defintely get an additional battery as Murphy's Law will dictate that you film for an hour with no action, and as your battery dies, you hit the motherload of action... the spare battery is essential...
They are great tools, and can really capture some incredible footage! You never have to reply on your buddies filming you which is great!
The only negative for me which Dan touched on is the fact that because of their design, the underwater footage is not pin sharp in focus which is a pity... I know that GoPro are currently working on an adaptor of some sort to sort this out...
Definitely recommend one, great tools!