I've not used any diabetes apps but with relation to carb counting I use MyFitnessPal. You can scan the barcode of your food and it can work out the exact carbs for most meals, it even adds it up for you and it's a godsend if you're trying to be strict with your counting hope this helps x
I love myfitnesspal, it great for scanning and gives good info on the whole....
Be wary though.... It doesn't always give the values... Waitrose quiche the other day it had some values but no carbs... It was 16g. Normally it gives you an alternative suggestion if it has no data for a product or it says no info... On this one it gave gobbledy gook for the data...