I bought a diversity monitor for $170 because I was tired of being tethered via cable to a monitor from my Fatshark goggles. The monitor I used with the Fatsharks was a 7-inch from readymaderc. Very clear and crisp image.
In hindsight I wish I'd gone with a Black Pearl as I'm not that happy with my diversity monitor. I haven't been able to compare my present monitor side-by-side with a Black Pearl but based on reports I've read, I'm guessing it would be better. But... that is just a guess.
I also bought a cheap DVR for my monitor and I'm not happy with it -- very low resolution, poor contrast.
What my experience tells me is to listen to that old cliche: you get what you pay for!