Well, that's 300k of gzipped code, so while the bandwidth isn't huge (300k is barely a large image these days), that's a ton of code to be parsed, and might be too much of a CPU hit for anything mobile.
I'm sure it's fine for a SPA, and for a mobile app it's a total non issue. Actually I'm planning to use it for one with React Native myself.
Luckily, people will probably not be including the full compiler lightly; I just wanted to point out that it's not as cheap as a jpg of the same size would be, an impression I thought the parent comment was giving.
On the other hand - in case of single page webapps it would only be loaded once and could be made to load only once thanks to browser caching.