[pixelesque]

I personally find Fastmail's spam handling a lot worse than GMail's: and I get a lot more spam in my GMail address, due to it being a 22 year old address, which I still use for initial sign-ups, before then changing account emails to my fastmail one after a few months.

Very likely a lot of the difference is the types of email each address is getting.

[nopurpose]

First time I hear about signing up then change email trick. Does it help reducing spam?

[pixelesque]

I'd like to think it does, but honestly I have no idea as I have no way of comparing to not doing this.