As both a Garmin and Funkwerk dealer, there has been virtually no difference in reliability until the present situation, where the Funkwerk units, designed, tested and approved by EASA and EUROCOM have problems in areas of high interrogation density. So much for standards.
After testing modifications and flight trials there is an EASA approved modification, following which serviced units will have the AD withdrawn, a modified AD is in the pipeline.
http://www.funkwerk-avionics.com/cms...eInfo_05_E.pdf