Is this on the Gmail web interface or on the Android app? I remember ads in the web interface that are placed above the message list for a while now, but putting them in the app where screen space is scarce would be an awful experience. If that happens I'm switching to Fastmail. Incidentally, does anyone know if Fastmail lets you pay for several years in advance?
However in Gmail I feel like I'm less likely to accidentally open one of the ads.