I tend to agree - the ISRU components are too awkward to use in most of my ship designs, especially the weird frisbee. At the moment, quite late in my playthrough, I've basically ignored the KSPI ISRU and used stock ISRU to mine liquidfuel to run in a thermal nozzle; even with the soot mechanic, it works just fine, and the ability to downscale the stock ISRU to 1.25 means you can side-mount two of them, and avoid really tall (and easy to topple) lander designs. This is kind of a shame, as I've totally ignores the methalox and hybrid rockets. The KSPI 2.5m stack part is really only useful with scoops, and once you have thermal nozzles, you can just run off the scooped gas directly. I would definitely like to see the KSP stock drills able to feed the 2.5m part for use on vacuum worlds. The ability to downsize the 2.5m part might be nice, but was not a big problem for me because it's height is reasonable; then again as noted, I frequently downsize the stock part to 2x 1.25m. The KSPI 3.75m part is too big. I don't have a use for it personally, given the type of craft I build. The ability to vent tanks in KSPI without another mod would be handy; when doing ISRU, a few of those empty tanks are handy for intermediate products that you then discard (leftovers from differing reaction rates). The stock ore carrier can be vented, I note.