These dongles are marginally useful but suffer severely from lack of input filters and gain distribution problems.
Probably fine for the intended application but in a dense RF environment intermodulation products make listening challenging, particularly if anything more than an inefficient antenna is used.
Even the better dongles, such as the Fun Cube Plus, with input bandpass filters are prone to overload, to the point where setting the LNA gain at maximum negative value (minimum gain) is necessary, and sometimes mixer gain and post mixer gain also have to reduced.
Been there, done that.
Yes, of course they are not in the same class as software-defined radios from Flex Radio Systems or National Instruments (the USRP).
But what do ya want for $15? LOL
They serve many purposes, the least of which is introducing people to the world of signal processing on a PC with free software.