I have free grandfathered Google Business Plan, including Gmail, but on my domain. The moment Google decides that I have to pay for it, even if it's 0,01 € per month, I'll be moving to another paid service.
Why I didn't do it myself, pure laziness, but starting to charge would be a kick in the right direction.
No, you should never entrust your personal data to something free. They keep the customer happy, so if you are not the customer you can't be surprised if they don't keep you happy.
I've been on fast mail for 10 years or so. I'm happy.
With GMail I got no spam in my inbox ever (but still lots of junk email from merchants and political campaigns).
With FastMail, I'm getting maybe 1 spam per week that doesn't get filtered properly. (And it's always from the same domain so far so at some point I'll set up a rule.
For search - I am not a power user and only search plain strings without ever clicking on "advanced" to filter on specific attributes. But every search I've run in FM has so far returned what I was looking for.
Not GP but I've been using FM for about 3 years now. I can probably count the spam that has got through their filter in that time on one hand and the same for the inverse of legitimate mail getting caught in the filter (each time it was admittedly sites on the sketchier side of the net).
I can't speak for search as I've probably only searched a couple of times but I found what I was looking for so it's probably fine?
Why I didn't do it myself, pure laziness, but starting to charge would be a kick in the right direction.