My personal experience has been that exhaust systems typically rust out from the inside as a result of the slightly acidic condensation from the exhaust forming on the cold steel. On the Abarth and on one of those 'Midas type' systems I had installed on a 745 (bad choice made in a hurry) by the time the hole poked through to the exterior the inside was a goner. As such, I personally wouldn't bother with exterior protective coatings on the exhaust system.

If you drive in winter conditions in an area where they apply a lot of salt on the road then surface protection might be useful; but, under those conditions you have to worry about the exhaust system outlasting the body on a 140.

If you purchase the Simons system, be aware that they use the original Volvo style double doughnut hanger on the tailpipe. Those particular rubber doughnuts are not what they used to be in terms of durability. The original on mine snapped after about 5 months resulting in a lot of banging of the mount. Two replacements snapped in quick order resulting in me replacing the complete hanger assembly with a flexible strap type hanger. The much larger rubber doughnuts that suspend the two mufflers have not been a problem