Diamond Haze is a UK 'brand' of e-cig. They used to be overpriced and junky.
However, these days they are relegated to ebay and less well-known vendors. The stuff is probably about average price but cloned off other brands so I can't see it being high quality.
More importantly, if you enjoy the tank (there is no reason why not) how much are the coils? I use Joyetech coils which cost £7 from China or £10 from ebay/amazon/nice vaping shops and these could easily be £3 each (sometimes more!) from unscrupulous shops.
Selling dodgy/expensive coils for rare (as in, not mainstream) tanks is ugly money.
You might consider just getting a mainstream tank.
It is 99% likely all the tanks and batteries/mods will fit together.