Hi @andy, apologies for late reply.. our mailing system had some trouble so we didn't get a notification for your post. Corrected that :)
Tto send a note to say gmail, please use the share option and select a mailing app you have on phone .. like gmail.
Premium upgrade unlocks many features otherwise not available in the free version. It will initiate billing when you click it and will ask you whether you want to confirm paying or not. You will not be billed unless you click to proceed. The billing system is from google so its 100% safe.