The interface is easy, clean, and no-nonsense. However, don't read that as intuitive. The main issue with Acid Music Studio 9 is getting up to speed with it. See all: PC Advisor Software Downloads.
The steep learning curve starts with icons that are tiny and not always readily indicative of their purpose. I found myself digging into the help file almost immediately to figure out simple things such as how to show the piano roll in the MIDI editor and dock a window for use as a pane - a rather finicky operation. I could go on, but after a few minutes trying to intuit Acid Music Studio, you'll fully appreciate why there's a "Show me how" function accessed via a tiny unintuitive icon at the top of the screen. See all Audio/Music software reviews.
Still, Acid Music Studio offers outstanding capabilities for a program that costs only £38. There's full-featured MIDI/audio recording and editing, support for both VST instruments and effects plug-ins, and Sony provides many of its own effects. There are even folder tracks so you can group and hide your vocal, rhythm section, etc. Powerful Studio One didn't get that feature until 2.0.
Sony Acid Music Studio 9 compares well not only to similarly priced programs, but also with those that cost considerably more. It's feature-rich, has a light disk/memory footprint and fast, and once you know it, it's easy to use. It's getting to know it that's the rub.