Get it, if and when you become serious. Or, when you decide you want to make money at the game. It's $100, that's a huge chunk of most peoples starting bankroll. If you don't know how to profit at the tables without a HUD, getting a HUD really won't help you much.
My advice- Don't get one, stick to playing fewer tables and try to develop your own concentration, writing notes etc, gaining experience. Don't get one until you know what it does, and what it can do for you(how to interpret stats). I really think people get HUDs because they know good players use them, and think it's some magical device that will instatly mean they will profit at the tables. It isn't, it's a guide, you still have to use your brain, unfortunately.
Remember, if you buy a HUD, be prepared to think about the other costs assosiated with using one correctly. There's a fair bit of time you need to put in, and also probably some coaching, or a training site to help you get the most out of it. So that $100, could easily turn into $2-400 if you also get coaching.
So you have to ask yourself, will i make this money back and then some? If not, then it's a wasted investment, you may as well have flushed that $100 down the toilet