Oh, Ok, so it isn't suspending when you have a hypo but before you get there because it knows what direction your blood sugar is going in. That's good.
Have a look a the 64 day 640G series of Video diaries that John Pemberton did on life with the 640G. I think episode 5 and 6 give a pretty detailed but user friendly explanation on how the Smart Guard feature works.
http://www.mm640g.blogspot.co.uk/2015/02/smart-guard-more-detail-explanation.html
All I will say is I have had my 640g for 7 weeks and Smart Guard rely does rock, yes I might have dipped below 4.0 once or twice but generally it just don't happen. You have to do something pretty silly i.e. over bolus for a meal or do a load of exercise that you haven't allowed for.
Its changed my whole perspective on getting the CGM's sensors with the older Veo I couldn't really see that it made enough of a difference to me to try and self fund. Yes they worked but all it did was turn the pump off at a set level, that might seem goo but its very basic as it dosent take into account what you BG is doing, and by that I mean its no good switching the pump off if you BG is dropping faster that a free falling sky diver its way too late. The 640 how ever does take this into account and depending you BG turns off before you get too the level you set, thus its allowing for the fact that you will go lower than the point at witch it turns off. Totally brilliant. Add to that it even turns the pump back on once you are rising and more than 1.1 above the limit you set it to turn off. I am no expert just totally amazed at how good it is, add to this all the alarms it can make if you want there is no way you don't know that you are about to jump off a cliff.
I am pretty luck as I also have good hypo awareness but this just helps you out.
Now even my wife says she cant see how I can go on without self funding because its literally changed everything.
If you have the time watch the Videos that John did, they explain much better than I can.