I bought a litre from Terrain Tamer a few years ago and still have half left as I don't dose it every time I fuel up. If buying something like Flash Lube its better to buy in bulk from somewhere like Terrain Tamer or other truck parts businesses as it works out a lot cheaper than buying the 50ml and 250ml bottles from Super Cheap etc. Bulk sizes come in 1 litre, 5 litre and 20 litre drums. Can't remember the prices now but if using a lot its worth buying bulk. I have started using it every few tanks as of late last year so when I run out it will be time for one of the bigger sizes.
The dose is 1 ml: 1 Litre of fuel so its easy to measure and does work at keeping the motor running smoother. I read on another forum that someone had seen the material data sheet for the stuff and it was basically mineral two stroke oil with some shellite mixed in for the cleaning agent. It's pretty mild though so can use it often.