The IATA Guidelines for the new MPL (Multi-Crew Pilot Licence) pilot license, the new gold standard for airline pilots include UPRT in a big way. It doesn't recommend UPRT, it mandates it. That's the word they use! Interestingly On-Airplane UPRT is listed as a "must" and put first in the recommended sequence. Advantages of On-Airplane UPRT are clearly stated in this new IATA document.
It's interesting that Europe seems to recognize the value of On-Aircraft training more openly than the U.S. FAA but actual On-Aircraft UPRT providers are found for the most part in the US!