I've used SyntheSIZE before and it's great. But, I've never tried Shotgun, until recently.
Of course, that's because I'd have to give up my infant son to buy it. But, I just got both for around$20, thanks to my gym's "75% off" clearance rack.
The Shotgun is normally $50. I bought it for $12.50; SyntheSIZE normally runs $40 or so; got that for $9 and change.
It's supposed to expire by the end of this month; but I suspect most if not all of it will be gone by then.