The Proton is a very well thought-out instrument. The patch bay is excellent, the modulation possibilities are extensive, and the waveshaping options give it a wide tonal palette that can move from classic analog warmth to more modern and aggressive textures.
Having two oscillators with their own filter paths is a strong design choice. It allows for complex layering, interesting stereo movement, and detailed timbral sculpting that you do not always find in compact semi-modular synths. The routing encourages experimentation, and it is easy to go from structured sounds to more exploratory patches.
I also appreciate that this is an original Behringer design. It does not try to be a clone but instead offers its own identity, which is refreshing in a market full of recreations.
That said, speaking personally, this is probably the unit I use the least among my setup. Part of that might be because I already own instruments like the Neutron that cover some similar ground, and I simply have not spent enough time pushing the Proton as deeply as it deserves.
But every time I power it on, I recognize that it is a serious synthesizer. The sound is solid, modulation is rich, and there is a lot of potential waiting to be explored. With more dedicated time, I am sure it could easily become a centerpiece for many producers.
In short: maybe not my most used machine, but undeniably a very good one.