I've been using TS-808 for years now and it has always gotten me what I wanted: 808 sounds. The live synthesized audio provides more variation and liveliness than static one-shot samples and the controls on the synthesis provide more control than the largest of TR-808 sample libraries.
The multiple outputs available in TS-808 is greatly appreciated and frankly necessary for modern processed 808 sounds.
It has the GM Standard mapping for MIDI so there's no need to rework MIDI scores or MIDI drum kits, and it also has a more compact 16-note range above that at C5 that I personally prefer using for programming rhythms.
A minor detail that I really appreciate is the ability to type in the values for knobs rather than only being able to turn the knobs with a mouse. Not only does this let me obsess over my sound, it also lets me enter values that exceed the limit of the knobs for wild and impossible sounds that still operate based on emulated circuitry.
The UI is beautiful and uncluttered, designed by Limeflavour who does great work.
Finally, for free? It blows the hundreds of paid TR-808 sample packs straight out of the water. It's an elegant solution to anyone's 808 problems.
This remains the best freeware 808 emulation that isn't sample-based.
Does it sound like an 808 is in front of you? No, but neither does Roland's own reissue. If you want to spend $0 and you are modulating/automating enough to require a synth over samples, this is the one.