I went ahead and purchased the MiMi with the spring coupon and I had a lot of points saved up, so it was a steal. I'm very, very satisfied with it. Personally, I think the vibrator in the MiMi is much superior to the one in the G-Ki: stronger, rumblier, and lower frequency/pitch.
The G-Ki I had did have a minor defect with the charging mechanism—it would only charge if pressure was applied, so it would not charge unless I actually scotch-taped the charger to the G-Ki. That might be why it would get very hot after being on for only five minutes or so. I'm happy to say that the MiMi does not have this issue at all; at the most, it will get mildly lukewarm after being on for thirty-plus minutes.
After trying the G-Ki, I did not think I'd buy another Je Joue product but I have to say the MiMi is so good that it has redeemed the brand for me.