There is no question that the SmartCafe mug is a brilliant device. I have owned and used several over the last 5 or 6 years and cannot imagine how I would enjoy my morning coffee without one. There are hundreds of reviews telling you how fantastic the mug is so I'm not going to repeat all that here but I do want to answer those few that keep complaining about coffee grains in their coffee and the size of the cup.
Here's how I make my perfect coffee. The aim is to keep all the coffee grounds below the fill line. Remember, any grounds above the fill line are NOT trapped by the plunger:
1) Before you start, make sure the cup is DRY inside. That will prevent coffee grounds sticking to the sides of the cup and sneaking past the plunger.
2) Put the coffee into the bottom of the cup - easy if you follow (1)
3) Add the hot water GENTLY - no splashing grounds up the sides - and most important ***FILL TO A LEVEL BELOW THE FILL LINE*** - a centimetre or so below the fill line should be OK
4) Stir GENTLY - keeping the liquid and grounds BELOW the fill line
5) Wait for 30 seconds or so to allow the coffee grounds to start to sink
6) Put the plunger into the cup so the filter just goes into the liquid and seals against the sides of the cup
7) Add more hot water, filling the cup as much as you like. Now that the coffee grains are trapped below the filter you don't have to worry about the fill line. No need to be gentle now either, you want the extra hot water to mix in with the rest
8) Allow to brew for whatever time suits you and your coffee, then push the plunger down GENTLY. If you push too hard and too fast you may get HOT coffee squirting out of the cup.
9) The end result is a FULL cup of perfect coffee, free of coffee grounds.
It's not as complicated as it sounds. Just common sense.