I use a Speed Box II on my 1Xpression. I had the Xpression for about a year before adding the Speed Box. I didn't think it would do much and wouldn't have bought it if it weren't for the 30 day trial period I got. It made a huge difference in my system. It took my table to the next level or two. After owning it for about 2 years or so, I unplugged it to see how it would sound without it. It sounds awful in comparison.
I've heard a bunch of systems with outboard speed controllers. Every one of them had a profound and positive impact, without exception. I haven't heard the Speed Box and Speed Box SE side by side to say if its worth the extra money. Most online places offer a 30 day return policy. Maybe buy both and compare at home? Music Direct carries them. Not sure of where you are though.