I contacted Mechman and received the same response for my 2016 iM, don't know if the Corolla is different, but with a little more digging and contacting other companies, I settled with Singer Alternators. Great guy, very good customer service and good reviews. I purchased a 240 amp neon green powder coated. It was supposedly a direct bolt on, but he mentioned to get a shorter belt or create a new top bracket, I just went ahead and got a slightly longer piece of metal, marked where I needed to drill holes to mount and done deal.
No significant drops in voltage on low frequencies and no slight dimming on my headlights anymore. Definitely give them an email