Factory fit is LED indicators Craig. The appropriate flasher is therefore already in place via the TSM module so your concerns are not valid.
FWIW I used the 55mm reversing light variant from same source to provide this feature on my M3W. I also used the same type of plastic pod so know it fits after removing the three mount lugs.
ETA: The Dasteri units you linked to look the same as Car builder solutions ones, even down to the lugs you have to remove. I would suggest either would work fine so it comes down to price and availablity in the USA.
