I endore these a ton and so do many others. Sadly, some vets (shame) are posting links all over to clones and counterfeit ones. So a public service to new people:
Vivi Nova: Get the 2.5. Make sure it says that, the older ones melt with juice and suck in general. Vivi Nova 2.5 or don't buy it. I buy mine at surevapes.
Vivi mini: Gotvapes has them (cool ego collars, too). Make sure it is an approved vivi mini. Some vendors sell a clone for half price which does not work with the standard heads which makes it so cheap.
Wherever you go to buy: official vivi mini and vivi nova 2.5.