Considering Skitarii have Haywire up the wazoo, some fairly impressive weight of fire rules and the Cult have kinda D-weapons on their troops, plenty of ridiculously tough and hard hitting models, they feel like a simple army from my first impressions. Few tactics on most of the models other than 'get in range and kill' while the Skitarii have some good choices for placement to make that one critical sledgehammer blow where it's needed.
I don't think there's a way to get around buying both books. Luckily they're cheaper than other codecies, but they both bring some very good stuff to the table. They're a powerful selection. I don't think they'll get lost in the least. But since no one has models from the previous edition of them, new release obviously, there's still time needed to play test them, find what works the best and how to maximize the ridiculous things available.