I looked into this around the same time as Cilnipidine. As you pointed out, adds a third channel, T, so I expected it to be superior.
The TLDR is Benidipine was kind of a commercial failure, It’s ability to block N channel is orders of magnitude weaker than Cilnidipine (which has relatively equal strength at L and N). So you lose all those great benefits N blocking provides.
Benidipine has much stronger L channel blocking, like Amlodipine, and because of that the risk of edema is much higher than Cilnipidine.
Finally, Benidipine’s unique T channel blocking does help prevent progression of (diabetes driven) chronic kidney disease. It’s much better at this than other CCBs. Basically Benidipine has become a rarely prescribed niche CCB, primarily for diabetics with chronic kidney disease.