I'm trying to learn another language in Memrise (French) I think it's a useful site to be familiar with the chinese characters and be able to read chinese on print but if you want to learn how to write, a formal lesson is required as I see when I hired a tutor. The print form and the written form ( as we write in on a paper) is quite different. But I love memrise too although I read somewhere that it's not 100% accurate as anyone can contribute in this site.