TBH, I can't see the point of having four channels. Most of the time you want to inject a signal into a system to test things like filter performance, distortion, etc. Then you'd be using one channel. If you used audio, you might need stereo, but four channels? My ideal sig gen would be <$100, have a minimum a 5Vp-p swing (ideally 10Vp-p upwards), be earth referenced (through USB or external plug pack), and be capable of sine - anything extra like arbitrary is a bonus.
They need some RAM on that design so they can load arb waveforms in.