The GTX 33ES is a Mode-S extended squitter transponder vs the GTX 327 is a Mode-C. So you'd get 1090MHz based ADS-B out. Your GDL88 is 978MHz, which good for US only and up to 18k feet. Additionally if you care about being tracked (some folks really don't like it, some like to be followed by their families and such) the various flight trackers have considerably more 1090 coverage than 978. Additionally 1090 based ADS-B does not support anonymous mode like your 978 does if that matters to you (there is the FAA PIA program, but there are hassles and limitations with that). So it really depends on how you look at it, as well as your current and planned operations, as to whether it is a benefit or not. Also, you'd still need to keep the GDL 88 for your ADS-B in. If you wanted to save some weight and get rid of both the GDL88 and 327 (and keep same capabilities), you'd need a 345(R).
