Well I've been using the 'Expert' for a few weeks now and I'm pretty pleased with it. It took a while to get the levels set up right and to understand how it was making its calculations but as of now it's making some pretty good bolus recommendations for meals and more often than not I'm just confirming them.
In a little while I'll do more of a full review with a slightly more considered account of my experience, but I'm investigating a slight oddity at the moment and want to get my head around it before I write that.
There is a line on the Expert's display which reads 'Active Insulin'. According to the blurb this gives you an estimate of the amount of working insulin you still have on board based on the timing of your injection and the figure you provide for insulin duration (in my case 4 hours). Except that it isn't doing that. Well not for me anyway. In the first week I can dimly remember seeing Active Insulin numbers which matched quite closely to what I would expect. At least once I tested after a meal and thought, "Well it's a bit high but I've still got a unit on board so it will come down into range soon enough."
Later I began to notice some very low 'Active Insulin' readings around 2 hours after a meal which did not seem to correspond with the amount of insulin that really was active at that point based on what my BGs did subsequently. Over the weekend I ran some tests to try to work out what sort of curve the device was using to plot the fall-off in insulin activity. I wondered if it was weighted to having a higher proportion of the dose being used up in the first few hours. This does not seem to be the case either... In three separate tests the Active Insulin was displayed consistently as either 0u or 0.1u at 30 minutes, 1 hour, 2 hours and 3 hours after a confirmed bolus of 4 or 6 units.
I've emailed my DSN to see if anyone else has had this problem. I may also drop Roche a line to see if they can shed any light on it.
I'll let you know if I hear anything.
Update: Active insulin explained - read the 'comments' below
Update: Accu-chek Aviva Expert Review - One month in