I've got nothing but good things to say about exhaust brakes. A lot like your loads, I tow 3-7k regularly, as much as 13-14k from time to time. Like some of the others, I run with it on whenever I can, trailer or no. I wouldn't be without it. At higher engine RPMs, like above 2200, it will feel like a reasonably firm application of the service brakes. The higher the RPMS, thr firmer it will feel.
Two cautions --
1) Do heed the advice to shut it off when you're on an iffy surface. You don't say where you live or drive, but in my area, hat would be rain slick or icy roads, loose gravel, etc. Oh yes, and on dry sand left on the road after the ice and salt have melted away.
2) If you're going to install it yourself, be careful of that nifty little gasket, if your kit has one. My e-brake housing did not have the alignment pins on the flange that also hold the gasket in place, and I wrecked one trying to get it in and clamping things up. If you find the same situation, try getting the brake in position, and supporting it from below. Make the gasket installation your last step before binding the joint down with the clamp. In any event, treat that gasket gingerly.