For Provari when battery goes down 3.7V, it is able to maintain the voltage you set in...like for example you vape at 4.2V and the battery capacity is reading at 3.6V(means batt going low), Provari will have the power to push the battery to 4.2V therefore you dont have the lack in experiencing different vapor production when the battery goes low.
Lavatube is good, but it cant push the battery up like provari...once it reads below 3.7V, it will fire according to the voltage it has left in the battery and not the voltage you set(in that case the 4.2V) , so therefore you would experince different vapor production when the battery goes down