New Coil-Over Conversion Suspension
... "Only" 3/16" plate with no backup support.
My concern too just looking at it as a mechanical engineer. The spring mostly puts a tensile load on the upright, but the lateral force is still high, compared to the thin section at the bottom of the upright where the bending load is highest. But then I haven't run stress calculations. One would need to design for metal-fatigue life since it sees repeated loads from every bump, and how many potholes the car will hit is hard to guess.
As example, one can buy torsion springs for a garage door with infinite fatigue life, but twice as heavy and costly so most people select smaller ones and live with the life. One guy posted a web article discussing his experience. He has 4 garage doors at home, so much spring-failure experience. He found when the springs break quite predictable, despite fatigue failure being a bit random. He had to replace a spring about every 10 years (door opened at least twice per day), with the size he chose. Ran across that while researching fixing my broken spring. Another example, I installed an after-market AC bracket in my 1985 M-B 300D. The guy fabbing them was a regular on a web forum. Looked rugged w/ 1/2" steel plate, but I found it had cracked thru in several places after ~2 years, so it couldn't keep the belt tensioned anymore. Whole-lot-of-shakin-going-on in a diesel engine, so even OE parts typically crack (engine-mounted air filter bracket, turbo oil tube brackets). TBD if the upright in this suspension will suffer similar cracks.