I do know people who replace tanks every week, but I think the shortest time even a cheapo clone one has lasted me was 3-4 weeks. As Polter says, you can prolong the life by washing them - rather than fiddling about washing then drying mine, I just soak them in water for a day then let them dry naturally on the windowsill, and use a spare meanwhile.
However as Polter says, the GS-H2s are well worth getting as they are IMHO a better vape than the completely disposable CE4 type which came with your kit and you can just replace the atomiser part rather than the entire tank. The e-bay seller she has linked to is the best value any of us have found (bar importing from China!) and everything I've had from him is original not a copy/clone.
If he finds he does get on with vaping, the next priority will be to get a spare battery. Not a lot worse than finding your battery needs recharging just as you're about to go out & not having a spare (or 3
).
The Hangsen liquids are OK, but nothing great. Chinese imports, pretty basic, safe but nothing special. Over time it can be worth looking at some of the UK made liquids as they tend to be a bit nicer, then of course there are those made by the specialist "boutique" liquid makers like Triphammer & Alchemist's cupboard (mmm Pear Drops
)