Pete, I will be surprised if you get much in the way of useful responses to your query, mainly because (thankfully) so few of us will have had cause to use them and of those that have needed to use them for real the outcome is either good or bad. In either case, there are other major factors that will have determined the outcome. Thus for the relieved and happy ones who life saving efforts were rewarded with a survivor, their chosen model will be flawless. For the others they will not be as enthusiastic. I suppose therefore that the only persons who may be able to give an opinion based on more than a unique or very rare use are paramedics, nursing and medical staff. Sorry for the pessimistic response.

Thanks for the comments and all useful (even the pessimistic one hehe) To SteveDM - your comments about the auto/semi-auto is valid, though staff training is constrained by insurance required 6 monthly refreshers! I'd also not considered that there may be an interchangeability issue for the pads. Thanks again Pete

See also this: https://www.resus.org.uk/pages/AED_Guide.pdf which makes it clear that, although having people trained to use the defibrillator is excellent, if no one is available when the defiv is needed, then anyone can follow the instructions and use the equipment, without fear of litigation or blame if their attempts are unsuccessful.