It's difficult at all to get used to using the M-Audio Oxygen 49. The feel of the keyboard itself isn't great but it's suitable for laying down parts as long as you're not looking for the feel of a true piano. The nine sliders and eight knobs are all assignable to just about whatever you want, and it also has transport buttons which is always nice to have. It's got everything you need but at the same time it's not convoluted and it's very easy to use. I don't know that a manual is necessary at all here...
The M-Audio Oxygen 49 is pretty much the perfect MIDI controller for those on a budget. It's not too fancy and isn't at all the best of what's available out there, but it will certainly get the job done most of the time and actually has a lot to offer, especially for the price. I don't own this at home since I have the M-Audio Keystation Pro 88, but I've used a few of these before in different studios and they are definitely adequate. The price is the best part about the M-Audio Oxygen 49 as it's affordable for everyone and it's definitely a solid controller.