Ive been using NIR cameras on drones to generate NDVI imagery for farm management for about 8 years, and have done about 100 000 ha of NDVI mapping. The short answer is that I haven't found a really great platform yet at cost effective price. NDVI is also quite an art in of itself and needs a fairly good eye and understanding of the crop you are looking at. Most of the NDVI work I have done has been with a Sensefly Ebee with Canon S110 modified NIR camera. I don't particularly like the ebee platform and its let me down many times but I still keep just because it the camera that goes with it good and generates good results.
I generally process with PIX4D and then work in Global Mapper to calculate the NDVI and adjust the shader to display the right colours for the and various values generated by the NDVI. remember that the NDVI is simply an NIR image that has undergone and algarythm which assigns each pixel a numeric value somewhere between -1 and 1, usually to 3-4 decimal places, that correlate back to photosynthetic activity. There are however many variables that effect the values, such light intensity, cloud cover, soil moisture, etc. This can to a certain extent be calibrated using calibration plates or light sensors integrated into the camera such as on the parrot sequoia, but I generally find it easier to simply adjust the colours and value ranges manually to suite the crop and conditions in the post processing. It's not very scientific, but i effectively calibrate the crop to itself and am able to highlight areas of good growth and areas of crop stress more clearly and in a way that will make sense the farmer.
I have tried the Sentera on phantom and was hoping that it would be a good option to replace the ebee, but I was very unimpressed with the results. the values did not make any sense to me and I had to go through various different software programs to get a meaningful result that at the end of the day, I didn't actually trust.
I also don't like the Parrot Sequoia, as the RGB side is really bad and the resolution on the NDVI is very poor. I have also heard that one of the online NDVI processing companies is sueing them because of the poor results they get from this camera.
I think the Mica Sense camera is about the best off the shelf option for NDVI and generates some very good results, but it is very expensive at around $9-10 000.
I have ordered an Xmission drone from Specialised Agricultural Services (www.specialisedagriculturalservices.com) who are the XAG guys in South Africa, and will be testing it out as soon as it gets here and will let you know what the results are like. it looks very impressive as it comes with a similar type camera to the Micasense but works of a RTK base station, and you can use the imagery to plan and execute crop spraying operations with the XAG crop spraying drones. check out the video at