Is there anything stopping you from using all three services? Why ditch Share*it if not?
Nothing prohibits me ( or anyone if you meant the generic you ) from using all three. But ShareIt takes almost twice as much as the others. You can easily say that $1 or $2 here and there makes no difference, but it sure adds up fast if it's your business. If there's an advantage I'm not seeing, fair enough, but I can't imagine what it might be. ShareIt don't have much of an affiliate network, so that wouldn't be it.
I don't know, do they offer something BMT and Plimus don't?