Hi Marty,
Class-Cs that benefit most from a heavy duty steering stabilizer, are shorter rigs. Your rig being 31 feet long, will still benefit, but the problem is less prominent to begin with, especially if your wheel base is longer than average (for your length) and your rear overhang is less than average.
With that said, our short under-24 class B+ has a Safe-T-Plus and it is effective. I cannot speak of other lower priced options.
Two negatives for our Safe-T-Plus are...
1) high purchase price
2) no life-time warranty (just a one year warranty)