Probably depends on what you want to accomplish. I bought a Kindle Fire HD several years ago and installed Cyanogenmod on it. Turned out to be a terrible decision. After days of fiddling and things not working and many hours of web searching, I began to suspect that I needed a "factory cable" and that the only way I was going to get one was to make one myself. (Which I did, wasn't too difficult, but information was sparse.) Then I discovered that I pretty much hated everything about Android, or at least Cyanogenmod 7. The aesthetics were bad (although Material probably helps a lot now), the icons were universally ugly (seriously, Google can't even hire a artist for its own app icons?), the apps were ugly, the scrolling was lame (I get that Apple has a patent on bounce, but the light blue highlight was both ugly and uninformative), the app store was filled with apps that had ads for 8 hours of developer work, basic things like calculators and notes apps were seriously ugly (and also were not included with the OS). I bought it partly to learn Android development, but I hated programming on Android because the API seemed to have taken the worst features of Java and the Linux UI, and was so full of inconsistencies that it made Microsoft's APIs look thoughtfully designed. Life is too short to use crappy Java APIs, so I ended up using it to read Kindle books for a year or so until the iPad mini got retina displays. Since then I haven't used it once.

If none of the above bothers you, well, the price sure is good. Just be sure to check how hackable it is, and how well your target OS runs on it.