Yeah, breast forms were great back in the day. I wore mine pretty much constantly before HRT, since the lack of breasts was one of the most powerful sources of my dysforia and they helped with that. I was pretty overweight at the time, though, so they didn't really look like breasts rather than just larger moobs. Still, helped me so I kept wearing them. I'm giving them away pretty soon since I've grown B cups in 10 months of hormones, so I don't really need them anymore. And it was actually just a few months into hormones when I had too much boobage for me to use them since they're designed for a flat base chest. So if you get them and go on HRT at a later date, you might want to find someone who might have use for them after you don't need them anymore.
As for cons, the only thing I can think of is that if you wear them while doing something that makes you sweat, it might cause a bit of a rash. But other than that, there really are no negatives outside of social pressures. The only time I've been sexually harassed was when I sported a beard and my breast forms.