I'll start the Cheap China Radio (CCR) thread by showing this picture.
That shows the sensitivity of the receiver combined with the channel rejection filtering in dB, which means, any signal value that is above the dBm curve plot will desense the receiver. You can pretty much extrapolate this curve from the last point where it is computed if no advanced filtering is used, like the SLR8000 repeater, with over 120 dB blocking for off frequency stuff, etc.. but unless you have one of those, most mobile radios don't have that kind of additional filtering. So if you live in an are with a noise floor of -50 dBm like I do, pretty much most CCRs will fall apart and desense so bad you won't hear squat. OTOH, radios like the XPR7550e, with super tight front ends, will effortlessly reach over miles when the CCR is deaf as a rock. This also shows why more sensitivity is not better, in fact, more sensitivity with a poor front end filtering means it will desense even faster.
IMO, the graph above should be pretty much definitive as to why the pricing is directly proportional to the selectivity + sensitivity on those devices: with the Motorola SLR800 repeater leading the pack at well over 2 grand, the Vertex EVX-5300, new, was around 600 bucks, the TM-V71a, is around 350 bucks new, and well, the GD77 CCR can be purchased new for 65 dollars on eBay.
And here is a very simple procedure to gauge a CCRs performance and if its even worth the expenditure.
1) First off, If no channel selectivity figures are offered, then move on. "These are not the droids you're looking for."
2) Now get the receiver sensitivity figure, usually measured in uV, but with this nice chart you can convert it to dBm at 50 Ohm, link here: http://www.repeater-...vity/dbm2uv.pdf
3) Knowing that any signal above the receiver sensitivity threshold (at any frequency) will desense the receiver you add the selectivity in dB at 25 kHz to the receiver sensitivity in dBm, pay attention to signage, the sensitivity is negative dBm.
4) Repeat the same for 12.5 kHz. Now, some brands show even narrower kHz dB figures offered. You can add it and find out, but that is usually not as important as the real selectivity for further away signals.
5) As a general rule, any signal received within the receiver frequency range (and in the CCRs even further than that) that is stronger than the 25 kHz selectivity value calculated will desense the receiver.
Have at it, and please, correct me if I made any mistakes.