Love 'em or hate 'em, guineas are unique among poultry. Ducks eat a lot of bugs, but a flock of guineas will target and terminate nearly any creature smaller than they are. Ticks are a special delicacy, and the reason most people would even consider having guineas. They are also superb watchdogs, with better eyesight and an alertness beyond any other poultry.
So those are the good things. But you need to know the not-so-good also. They are noisy. Not just a little noisy, but annoyingly so. They wander over great distances. A flcok of guineas can easily roam over multiple acres of land looking for food. So, they might spend a lot of time with your neighbors, make sure they are ok with that (mention the tick thing and they might be amenable).
Baby guineas are called keets and are more delicate than chicks for the first few days. After that, they are very active and grow fast. I usually keep them with slightly older chicks because even though they seem smaller, they are more aggressive and only larger chicks are safe with them.
Ours often dust bathe or sun themselves in the road. That is not a problem in a quiet farm lane, but next to a busy road, expect traffice losses. They are predator-aware, but vehicle stupid. They are also terrible mothers, though they try and can be quite fierce when protecting a nest.
Some people have reported that they eat honeybees, so if you have a hive, be aware they may consider any bees snacks, even your honeybees. The upside is they like ground nesting yellow jackets too, or at least we have never had them since we've had guineas on patrol. Ours often form lines and walk though fields, eating any bugs they find and chattering to each other as they go.