I worked in a very similar system for a very different company and I tend to think that a good reason to implement your own OCR models (if you can afford it) would be optimizing CPU cost. Tesseract can be quite expensive to run in scale, maxing out 100% for a simple page and taking about 5-30 seconds for full page extraction. Also, most Tesseract pipelines take entire PDF files for processing, whilst you could achieve better latency by processing pages in parallel and merge the results, as they suggest in the post.