The problem is that the 900 MHz class UART is only for use within the US below FL180. That's one of the reasons 1090ES is popular - if you fly outside the US or in the flight levels then 1090 is mandatory. Also, there are many Garmin transponders in service (the 330 is very common here) that can be upgraded to 1090ES for about US$1k if you already have a WAAS GPS, making it a relatively cheap option. You don't get the data 'in' that the UART provides, but XM weather is also a very, very common accessory.
Last edited by Tinstaafl; 17th Feb 2016 at 04:35.