I have been working during several weeks to convert an old good PSU I have into something decent.
I don't know how the high-end PSUs are, but, at least for the low/medium-end units, the drawbacks are not only the minimum load requirement and the lack of maximum current setting.
Usually, the switched power units like that only have a main transformers that generates all the voltages, therefore, they only have a feedback circuit to control the commutation on this coil. What that means, basically, is that for instance if you start loading the 5V line, its voltage will decrease meanwhile the voltage of the 12V will start rising. In addition, in my PSU, the 3,3V line is not used in the main feedback circuit, therefore, its voltage decrease quite quickly with the load if I have not something connected to the 5v or 12V lines (which are the ones that control the duty cycle of the PSU). Summarizing, it is cheap, it is good enough for a lot of uses, mainly if you need a lot of ampers, but it is hard to obtain a good regulated voltage from it if you do not modify it deeply. Therefore, maybe it is the best option for driving heavy loads, but if you only need some hundreds of milliampers, maybe you could build something even more cheap using something like: