FWIW I was able to successfully use tax-free shopping at 3 places (Loft, Odakyu department store, small leather shop in Tokyo station) on my last trip with the TTP card. Loft involved the clerk disappearing for about 10 minutes with my passport and card but then processing it without issue. Odakyu wouldn't look at the card and instead found an old entry stamp in my passport and just changed the year to 2020 on the customs form when they were filling it out (...) and the leather shop just asked me my landing date and wrote it in the form.

Still not seamless but I was able to get it processed everywhere I spent money.