Well, as Crossing Cambodia was in Mondulkiri last week, it was decided to look into this matter. The road is a 15 km section of the road between the main provincial capital of Sen Monorom and Bou Sra, arguably the site of Cambodia's highest waterfall. The terrain of the road is hilly with some flatter area'sand some steep descents / ascents. The company has done a good job, the road is wide and though still being graveled it is very passable. The tariff looks quite high especially in view of the charges for the nearly 200 km stretch of national highway between Phnom Penh and Sihanoukville. But the previous situation was deplorable, only passable with motorcycles apparently and big 4 wheel drives. The poster which the company had hung up at the toll booth goes a certain way to justifying their need for toll as a reward for improving the road.
Despite this it must be said that most roads in the province were in good, even excellent condition; with the exception of the main link road to Snoul (and thus the rest of the country) which was need of rejuvenation. That said it could be worse, but maybe a potential investor might want to invest in a new road?