Head knives are debated back an forth all the time. Some leatherworkers use them for almost everything and others can not figure out how to use them. If you are not sure, I would recommend you talking directly to someone that likes one and have them show you how it works. DO NOT buy a cheap one, you will just hate it and figure they are all worthless.
Personally, I use mine a little over half of the time. I have other knives too, and depending on what I am cutting I will switch back and forth. My recommendation, as a beginner I would recommend you using a box cutter. They are cheap and relatively easy to use. As you progress, keep your eyes open for a class or the opportunity to talk to an old leatherworker and see how he uses the round knife and go forward from there.