I would rate the Installer's Set as barely worth it when I got it at the $299 sale price a few months ago. Having had it for a few months now, I'm glad I got it, but I would not pay $350 (the price of an ETS 150) for it at this point. Maybe in 3-4 years, when I'm still working off the included bits, I will feel like it was a better investment?
EDIT: Let me just say, though, that the drill bits that came with the set are the best bits I've owned. Razor sharp and true. Combined with the T18, I can now do some operations that previously I would only trust to a drill press.