No experience with Bullfrog Cloud unless that is just their name for the Balboa WiFi module. If that is the case, I would pass. When I sold Marquis (2014-2017) the few WiFi units I sold had connectivity issues. There were times I could not connect to a spa on my showroom floor and other times when I could connect 250 miles away. We did move locations and change internet providers, and still had the same issue. I have seen other reports of Balboa wifi issues, so my guess is its on Balboa's end.
As for Connextion, I have sold 3 now in 9 months with Hot Spring / Caldera. I personally think it is more reliable, but comes at a greater cost. Connextion also alerts the dealer if there is an issue, so it is more than just an app that allows you to monitor the hot tub.