Hi there, I use an Omron Microair which I find is good as it is very quiet and compact. However, I dont like having to hold the unit at my face when having a bad attack, lazy I know!, and you have to keep tipping the unit up to keep the liquid to the front of the machine, allowing it to continue nebbing properly, otherwise it keeps stopping. I have just seen the new PARI Trek S which looks very good. I used to have a PARI walkboy many years ago and the new PARI model seems much more compact than this. Has anybody bought one?? It's often helpful to find out what other people think before buying one as they are expensive.