I got my Harmony Encore cart this morning and inserted the same SD card in which I currently use in my also-newly-obtained Atari Flashback Portable, and tried a couple of games on my new 2600 Jr. and it plays great, using my CX-24 7800 sticks in which I prefer to use on her. The response is quick, and I even played Pac-Man 4K as also Asteroids and the OG version of Atari Pac-Man (on the Harmony) and had no problems with compatibility with those, I'll do some more testing on her later on, but I am quite impressed, and now I hardly ever have to buy another cart (except for new homebrews from right here at AA) for either my 2600 Jr. or my 5200 as now I have BOTH the AtariMax 5200 Ultimate SD Cart, and now the Harmony 2600 SD Cart. That, the soon-to-be obtained AtariMax 8-bit Dumping cart and needed adapters (for 2600 and 5200), and all the gear I currently have for both units will come in pretty, pretty handy now that I finally have it,
Thank you AtariAge and thank you Fred Quimby!!!