"Diamond River has not produced good quality fruit. "
I would disagree with that. However, it could be a difference of climate/soil/care.
I have the kohala, biea keaw, sri champoo, and Diamond River. I probably misspelled those but, I like them all. The DR is the only one that produced this year. All trees are mature and last summer they all fruited heavy. So, this year they are taking a break except the DR (which also fruited heavy last year). The DR has two crops on them this summer. The one I'm eating now, and the next crop is still small but the tree is loaded.
It tastes like a longan to me. There is a slight taste difference between the variety, but like lychee, every variety taste good. At least to me. I don't know how you can say its not good quality fruit. I can't speak to your experience as I have also tasted bad DR before. That was because they were overripe and in fermentation. but, there is no way I would say Diamond River produces bad quality fruit. In my experience it has been great!
When it was first introduced in the mid 1990's it, Diamond River, a/k/a was the rage. Every one had to have one in the circles I was traveling in at the time. I planted two trees out and I know many others that planted them out as well. These were all in Dade and Broward Counties.......more in Broward though. My fruits were similar to others I tried from these other people. The fruits on DR were smaller, considerably smaller, than other cultivars available and had much lower flesh to seed ratios. If those were the only issues, that would have been OK with its later bearing. However all of the fruit that I tried and/or grew had a washed out flavor and just not in the same league as the other culitvars. It wasn't even as good as one of my seedlings....a seedling of Kohala. But, of course, that is only in my opinion and experience. Maybe my tastes are off. I'm just giving a warning that tasting first might be considered before committing the space to a tree planted out. I'm sure some people would consider me a Longan snob.
However, I am not alone with regard to this opinion. U of F reports as follows:
Varieties
There are numerous cultivars of longan; however, world-wide only 30 to 40 are grown commercially. Reliable bearing is the major production problem for longan throughout the world. In Florida, 99% of the acreage is planted with 'Kohala'. Other cultivars have been introduced, some for a long time and others recently (Table 1). A number of new and re-introductions including 'Edau' ('Daw'), 'Chompoo', 'Haew', and 'Biew Kiew' are under evaluation by several institutions and producers. However, nothing superior to 'Kohala' has been identified.
One of the recently introduced cultivars is named 'Diamond River'. This cultivar is from Thailand and is reported to fruit every year, be precocious, produce off-season, and produce a sizeable late season crop. However,
fruit quality is only fair and the tree is very susceptible to limb breakage.
See:
http://edis.ifas.ufl.edu/mg049