I have also read about them, but also haven't tried them.
I'm not likely to, either because they all require manual data entry. I have a meter, a pump and a CGM which all collect data that I can download and manipulate to my heart's content.
I don't have any need to have the data available on my iPhone, but if I did, I have other Apps I can use to view the reports I create from my Meter/Pump/CGM.
GlucoseCharter has a need food database to help with counting carbs, but for that I use Food IQ, which uses the USDA database - the same one I used to use on my Treo.
I think these Apps would be good for a gadget freak (me) who doesn't have a lot of other gadgets (not me) and doesn't like logging data in pen and paper (me) but wants to have the data available at all times (not me).
If my doctor used an iPhone, I might use one of these Apps to share data with her.