Apologies for resurrecting a rather old thread, but I thought my experience might be useful.
I've been T2D for years, but only in March after an angry meeting with my doctor did I start taking it seriously when she started me finger testing.
I quickly discovered the Abbott Freestyle ISF monitor and bought some. I have had a few problems with variable sensors but the data has been absolutely fascinating in terms of discovering what things do what to my body glucose levels and when I feel like when I am at particular levels. So am really interested in anything new that comes out as the Abbott works out at about $200 a month so especially if it comes in cheaper it will be interesting.
Apple are also working on this technology and Tim Cook was seen wearing a prototype last month. They too are focussing on "Wellness" rather than "Medical Device" so they can get it to market without going through the FDA.
I actually got to these forums because for a while now I have been sort of half heartedly toying with the idea of trying a keto diet (I've been vegan too since the start of the year making it harder but not impossible), and have been consciously trying to keep my carb intake down to between 50-100g and sometimes I do wonder if I am in keto.
My Freestyle meter has more frequently shown me very low (<4mmol/l) and I did a web search to see if being keto or just low carbs might affect whether your interstitial fluid reacts less than your bloods, or whether my sensors were just still playing up!
When they talk about "lag" incidentally, it doesn't so much flatten out as changes happen between 15 and 20 minutes after your blood changes. Sure, if you are suddenly very low and worry about hypo then they recommend you blood test before making decisions about glucose and/or insulin intake. But as a general tool to monitor what things you put into your body does to your glucose levels it has been invaluable.
Alas, the question that brought me here was not answered and is possibly an area for research - whether keto or low carb diets might make your ISF appear lower in glucose than it appears when blood testing. But I suspect it will have been quite rare for ketogenic dieters with T2D to have been using any of these products yet.