The best thing about beaconstack was their customer support! They helped us choose between several different platforms for our startup & they guided me through setting up my beacons which I had never done before (and have to do it all again).
It's super cheap compared with other solutions that offer more features but you can't get help from someone when things go wrong like issues sending your messages or crashes of app etc.. If anyone needs an easy way out - use BeaconStack not only because its free however also just install them now since there are some problems while installing due timeouts during setup process so try early else pay later :) Sending text message via WhatsApp integration works great if user has enabled notifications otherwise users might miss notification emails sent directly without having any idea whats going around at this moment ;).