IT'S THE ONE!!!☺ I've had a terrible problem getting my iTop Launcher to be the default  on my LG G4 Marshmallow phone. Have gone through several Default managers  which allowed me to set iTop as my Launcher -- but ALL failed. Instead  I just kept seeing the message block  each and every time I booted up my phone -- and exited any app -- to choose iTop ALWAYS. Nothing worked  nor did the instructions I followed from the web  how to manually do it. Thankfully  THIS app SEEMS to allow me to select iTop  once and for all.
March 09 2017