Setup does not require API key, which is nice. To see what font you want, you would still have to go to Google Fonts. However, nice. Once you choose a font, it lets you choose which variants you want to use.
Very laudably, combines all the fonts you want into one call to Google fonts. Also, for custom CSS, he consolidates that into one block.
Once you choose a font, all the variants for that font show up, and you can choose whic ones you want. This is terrific.
One thing, is that some fonts have a variety of weights—e.g., Open Sans has 300, 400, 600, 700, and 800. To have total control here, you'd have to write out more specific CSS instructions--but there's a place to do that for each font.
What's awesome is that at the developer provides a place where you can assign "generic" selectors, such as "p" or "h1" to a certain font, but also a box where you can apply specific rules.