Well... It's a multichannel sound interface. There's a lot of hype around Focusrite interfaces, and to tell you the truth the bigger part of this hype must be carefully bloated marketing brainwash.
They're not that great. Specifically the Saffire 40 isn't.
The "40" name is a swindle of sorts to begin with, as there're at least 16 less I/O channels (they plastered 16 channels of MIDI I/O into it - why?). Lightpipe connections are halved at 96/24, and then the optical connnection is only one pair in S/PDIF mode.
Really it has 8 combo analogue inputs (XLR/TRS preamp/bal-unbal line/guitar - though only the first two sockets work for guitar wiring, the interface has 8 microphone preamps). 10 analogue outputs (all TRS sockets, balanced/unbalanced). And electrical and optical S/PDIF (or Lightpipe).
The way it records gives the impression that the microphone preamps are gained low, while the ADC stage is gained high. Translation - it clips early with sensitive condensers (like Rode NT5, say), which is to say, most of them. We tested NT5-MP as overhead microphones on a drumkit, and they gave a nasty mute tinkling kind of sound for cymbals/hi-hat, whereas a Digidesign Digi-002 interface (the old thing) painted a beautiful ambiental overhead picture with rich cymbal and hi-hat detail. That about tells it. The Saffire 40 has a rather mediocre recording quality.
There is a workaround, plug the overhead condensers into the first two inputs (out of 8 combo preamp/line inputs) and enable "instrument" (read: electric guitar) mode. This then apparently switches the ADC stage into higher gain, gives the preamps (a lot) more headroom and allows for enough sensitivity for overhead recording. It's still inferior to the old Digidesign interface, but it starts recording ambience and details (no more clipping early and mute tinkles). The irony here is that the Digidesign interface supposedly has Focusrite preamps. They work beautifully, but then they must be gained right and the ADC chips are clearly superior.
The ADC/DAC quality itself isn't anything to write home about, if you want an approximation, it sounds like one of those Realtek integrated audio chipsets. Just balanced. Connected directly to the KRK RP6 G2 monitors via balanced, the Saffire 40 sounds dull (with some of that cheap digital hollowness) and lacking character. What fixed it was plugging the balanced outputs into a Yamaha MG-102C mixer, then plugging the speakers into the mixer (balanced, of course). This, in theory, shaves off the extra 20 or so dB of SNR the Saffire 40 has compared to the mixer, but it also kills the dullness. Maybe it's just showing how much uglier higher-res digital circuitry is.
The old Roland UA-1G interface sounds noticeably livelier than the new Saffire 40 (it is built on an AKM AK4556 DAC, while Focusrite never discloses what their codecs are). The UA-1G's still better for sampling, even though it has no balanced I/O and only two channels.
The bottom line is, something more expensive and better like a Mackie Blackbird or Roland Octa-capture would've been it, but then both are rather more expensive (almost twice the Saffire 40 price for the Octa-capture).