When you get your own binder, put it on and go shopping (or go through your/your family's closets) to find your own style that gives you a look you can tolerate. A lot of the bigger guys recommend layers and baggy clothes and stiff fabrics and buttonups. I personally look ridiculous in that style - put me in a big stiff baggy buttonup and I look like I'm wearing a muumuu. Or a tent.
What works for me (and I don't/can't bind completely flat, so it's not necessary) is the exact opposite of what they recommend: fairly close-fitting shirts in solid-coloured knit fabrics that do show the shape of my chest. I find it's best if they're short enough to show off my butt. And I have to be fairly picky, because I need them to fit correctly at the shoulders while still being wide enough at the bottom that they don't catch too much on my hips. I'm still working out exactly what's best on me, but it's definitely not standard trans guy fashion - it's probably best described as "conservatively gay."
Anyway, the particular binder you get will affect what looks best on you. I have several different binders that I wear with different clothes, although my all-round favourite so far is the 998 because it eliminates the need to camouflage the armpit bulges. Any correctly-fitted Underworks binder will give you a chest that can be passable if you pick the right clothes to go with it, so you just have to go experiment and find out what those clothes are.
A note on fit: The instructions tell you to average your bust and underbust measurements. That put me at a smallish Medium - but the size that actually fits me is a Small in the heavy-duty binders like the 997 and Tri-top, and an Extra-Small in the softer ones like the Cotton Concealer and the 998. Consider ordering 2 different sizes of the binder you like, one in the correct size according to the instructions and one a size smaller, and just returning whichever one doesn't fit.
