I've own GR3 for years...many, many, many years and was a beta tester for it, as well as GRLevel2 (no longer available). I've had GREarth from time to time on a monthly basis depending on the need for it. It's an outstanding product.
I was recently doing a comparison on the basic reflectivity product between GRE and GR3. The quality control of GRE's base reflectivity is so good when zoomed in, there's almost no difference between the two. Now granted, GRE does not have velocity products, dual pole products, placefiles, shapefiles, etc., but if you're looking for a great affordable product for reflectivity only, GRE is outstanding. Nice and stable.
Here's a screenshot comparison between the two:
(GREarth is at the top, GRLevel3 is at the bottom)