Jeremiah,
From having had a few Tekonsha's thru the years, all are about the same size! so get what you want, and install it!
One thing I have found as to "IF" it made sense to hook up brakes on a trailer. If the trailer weighs more than the payload available for the tow rig, put brakes on. They may not do a lot per say, but they do help some. Even a small trailer like you show behind the sorento, helps to have brakes on it with your 350! Trust me, I know! I had a bigger single axel towed behind a flatbed 350. Once I put brakes on the trailer, my brake mileage on the truck fronts doubled. From 10-15K per replacement, to 20-25K miles. This is daily city use with lawn mowers etc in the trailer. ABout 1500-2000 lbs total.
Just some more 02 from me, not that 02 is worth much these days!
Marty