Usually any lack of knobs is a hassle, but the P12 desktop is very economical and intuitively laid out. I was actually more annoyed that the Tempest doesn't have dedicated sustain and release knobs. That said, if you're really into jamming while twisting a lot of knobs, it could be an issue.
There's plenty of info stating what the P12/PX are all about & it's easy to spot the differences. One thing that you won't find plainly stated, at least on the official site, is that the PX has a more highly regarded filter based off the classic SSM2044 (the SSI2144).