I got Renoise six months or so before the Polyend Tracker. Much like @kasselvania has mentioned, Renoise is much more like a DAW. It is VERY complex. I’m still wrapping my head around most of the things it can do, plus I’m relatively new to working with hexadecimal. You can change the lines per beat in a song in Renoise, giving you micro control of notes and effects while maintaining something like 100 bpm. You can resample the audio of a whole track and chop it up and move it around with the sequencer effects. You can also have more than eight tracks, group tracks, etc.
The tracker is much simpler. 8 tracks. No resampling of tracks. (Now) 2 send FX. No hex code, so coarser refinement of your sample, wavetable, or granular manipulation. The lines per beat is fixed, so if you want the micro control I end up just doubling up the bpm (it goes pretty high, well over 300). Overall it is a much more limited experience.
That said, I use it now way more than I use Renoise. It’s pretty intuitive and fun, and I find the ‘limitations’ quite liberating creatively. I’m never finding myself reviewing a manual to figure out some much deeper trick, which I was doing with Renoise every time I opened it up. When I have something I like, I export the song stems and put it into the DAW of my choosing for further processing. It’s been a little glitchy here and there, but Polyend has been very good about updating the firmware in a timely fashion. And its nice that its portable with a power brick, if I don’t feel like working on a laptop.
Overall, I’d say I’m very happy with the purchase. If your looking for a more complex sequencing powerhouse I would recommend Renoise. If your looking for a fun, simple, portable, way to make tracks, I would recommend the Tracker. Also, Renoise is much cheaper 
