I'm the last person to knock the Airspys. I love em. I have two of them. But there is a caveat . Youssef will tell you himself that on 1090 mHz you need an external preamp. It's great that the Airspy has a bias tee [which I use] to provide power to a preamp [which I use].
Youssef has a Windows app and a Linux app to do ADS-B on the Airspys. Also, xDeco.org – SDR programs and utility for RTL2832 and Airspy
has versions that work with the Airspy as well.
Keeping all of that in mind, if you are interested in using the Airspy for feeding to FlightAware and participating in MLAT, you will need to run a version of the software that works on the piaware and make some adjustments. And you should be aware that when running the Airspy on a piaware kit with the best performance of the Airspy in mind, it is going to use significant CPU resources on the RPI. It could in fact use enough CPU resources that you end up having difficulties with MLAT timing as the CPU usage increases.
I run a Raspberry PI with piaware 3.3.0 and the latest version of the FA Pro Sitick, along with a DPD Productions ADSB-Out antenna, LMR-400 coax, an Uputronics preamp / filter ( HAB-FPA1090SAW ) and a Mini-Circuits power divider (ZAPD-2DC-S+).
The power divider has one output that goes to the antenna and two inputs that come from devices. One of the device inputs will accept bias-tee power and pass it up the antenna. I have an Airspy R2 hooked to it. The other device input doesn't accept power and I have my FA Pro Stick hooked to it.
The Airspy R2 is running on a stout Windows box, using modesdeco2 software (from xdeco.org). I use that to feed planeplotter and my VRS as well as to send data to ADSBExchange. And via planeplotter on that same machine I'm feeding data to various other places.
On the RPI itself, it's feeding Flightaware and ADSBExchange using the FA ProStick.
So, one antenna, one preamp/filter, LMR-400 coax, a power divider, and then Windows + Airspy + ModesDeco2 / RPI + Pro Stick.
The Airspy wouldn't touch the performance of the FA Pro Stick when I wasn't using the preamp. When I added the preamp, it now performs better than the my FA Pro Stick setup. Although I can tell that I still could use / benefit from more amplication at the antenna end -- and am sure the Airspy would perform even better if i could do that. I'm only using 50 feet of LMR-400, but I have many different adapters and pigtails in line -- and between those and the length of the coax, I'm likely losing a few precious DB.
I have never used a Diapason, but I am told that it performs great, partially due to the amp built into the antenna. And that is also why they ship it with the coax they do.
I've never used a RadarCape and can't say anything about it.