Whether they're manufactured by the same company or not doesn't necessarily mean they were manufactured in the same manner, i.e., in the same press. Clearly there is a difference. If nothing else look at the lettering on the battery connector. I think it's a battery connector issue as well rather than the cartos. I hope that it's as simple as wear on the batteries will make the threads loose enough so that "all" cartos go on easily. I can't see that it would make a connection problem, just a little freaked out at first because it's a gift for new vapers, and I didn't want them to have to worry about problems putting their equipment together. If given a choice I would choose the Hello over the EM Rivas. It's worth 10 bucks not to have to worry about it.