Why would you outgrow a trainer? I'm many flights away from being able to bring a trainer down the runway one foot off the grasss inverted, pulling up/down, climbing to an adequate distance, and flat spinning it back to near ground level. I still can't circle the field doing a continuous rolls without hesitation with my trainer. I still can't ........

And when I prove I can't, my trainer is much cheaper and easier to repair or replace than most other planes.

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added:
I got good enough that I didn't need a trainer last year. This year I have a 40 size and a 60 size. The better I get the more I like to get the trainer out to try new things.