Lemon still reminds me of a certain someone from Toradora, but maybe that is just me.
As far as size and hair length I can see your point. But temperament and basic ability, I think Lemon has her left in the dust. So only a few characteristics, and if the two of them were together, they would beat you senseless for making the comparison. lol I think that this show only has a couple character traits similar to any character from Please! Teacher, and Please! Twins, or other anime. I think they are relying on the story to make this anime a success, rather than plug and play character traits A,B,and C with character 1, and character traits X,Y, and Z with character 2, and so on.
I wonder if the creator was trying for a less controversial approach to the alien/ human relationship question this time. Taking the more 'natural' approach, so that people talk about the story more and less about the taboo relationship.