Today my son, who is now almost 7 months, leaned forward in his high chair seat, picked up his doidy cup with both hands, accurately brought it up to his lips, tipped it up and gave himself a drink of water. It was fantastic to see him do this for himself. (He then gave us both a shower by enthusiastically banging the cup on his tray, but nevermind, it was nearly bathtime anyway!). Seriously, I believe these cups are recommended as they encourage the development of facial muscles - needed for a child's speech development. You have to expect a bit of wet mess (and I wholly recommend those bibs with a fleecy front panel which absorb the spilt liquid brilliantly). And yes it is a little less convenient when on-the-move than a sippy cup, but I still think that a child's development - through experimentation and practise using a doidy cup - is more important than our own convenience, most of the time anyway. A child is going to use a mug/adult cup eventually anyway, so why not give them something similar but a little more manageable to start with? Goes very much hand-in-hand with baby led weaning principles I think, if you are folowing this approach, but anyone can benefit from using them.