I am just back from a three-week trip to south and southeast Asia. I have had the Diners card for years, but never did take advantage of the lounge access benefit. But this trip was different. I have used the following lounges:

BKK Louis Tavern Lounge (2 times)
KUL Plaza Premium Lounge (2 times)
DAC Ruposhi Bangla Lounge
ATL The Club at ATL

Getting access to the lounges was no problem at all. As one would expect, the quality of the lounges varied quite a bit. My favorite was the Plaza Premium at KUL. The food and drink choices were excellent. I can still taste the spicy noodle and fish cake soup in my mouth! Incidentally that was also the busiest of the four, but that may be a factor of the time of visit (morning). The lounge at DAC was not much to speak of, but considering the facilities in the rest of the airport, it was not bad at all. The BKK lounges were the most quiet, which was fine with me. All had pretty good wifi access.

Based on my visit, I will reiterate what I had said earlier, this lounge access benefit from Diners, compares very well with other cards. Sure Amex MR offers access to a lot more lounges, but it also costs a heck of a lot more. In the end, like many other things it really depends on your frequency of travel. Frequent business travelers should be able to justify the cost of MR. But if you only travel a few times a year and mostly international, Diners is an excellent value.