Yeah that is definatly alot different but as long as it works good i wouldn't be to worried. The heads may be hard to come by as i doubt regular vivi heads would seal correctly. Probably should stick with the vender you got the vivi from when ordering replacements.
I have 3 real ones, and yes, the heads are not the same fit, I tried one and it sits a lot lower so it won't seal to the top cap.
But I just ordered 10 replacement heads from the site I bought it from so all is good for a year.
One week I've been using it and I find it better than the real ones I have.
Even some of my mates like it so much they have all ordered a few for themselves too.
Bargin at $6 a pop, and with the bulk order it cuts down on shipping costs...