I may be reading this wrong, but the only annoyance I would find with their toolchain is that it seems like their true source is the FontLab files which is not open source. The readme says that you should be able to edit the UFO files and generate the FontLab files from that, but it doesn't seem to be the process they are using. It would be nice for the UFO files to be the true source rather than a derived one.
Unfortunately, doing TrueType hinting more-or-less requires FontLab. There are other alternatives that are being developed, but by and large FontLab remains the industry tool for building TT-hints. Part of this talk by Tal Leming (https://vimeo.com/album/3329572/video/123781570#t=457s) explains some of the interchange issues with TT-hint formats. Long story short, everyone has a slightly different hinting compiler, and they're all proprietary.
