It's a niche product, but a good one – Ribbons : Touch Instrument Review

I've felt conflicted about how I feel regarding Ondes. I didn't buy it immediately, but definitely kept my eye on it from Day One. Even now that I own it, I'm not exactly sure how to use it in my music. But if you watch some of the demos and like what you see and hear, I feel like it is a 5-star app with a unique interface and resulting sound. The "slider" interface is very attractive looking, but it's not really an "innovation" for this app. ThumbJam, Bebot, Figure, SynthX, and on and on have all used some variation of this control scheme, which works great on an iPad. Unfortunately, MIDI out control is not in the works at this time, but perhaps in the future. So the usefulness of Ondes will mostly depend on its unique internal sounds. I will say that the presets don't offer a huge array of variety, but there is a synthesis engine within your app, which is what differs it from something like ThumbJam, which is sample-based. So you make your own sounds. Really liked the slider controls and variation of "snap to" as you cross over note lines. You can have a meandering almost sci-fi sounding pitch, or snappier transitions that land on the exact note. It's a beautifully put-together app with some unique sounds, and I value it as much for its originality as the end "usefulness". I would not want this as my primary instrument app, but as an add-on for unique leads and cool atmospheric stuff, it's great.
Review by HouseOfHomuth on Ribbons : Touch Instrument.