The only person I know who has told me they are testing out premium is @shainemata. Perhaps he can update us all on his experience.
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The experience depends largely on how you use it.
In my opinion, what makes InLeo Premium worthwhile is getting priority in the For You tab of Threads. This means you get added to the rotation of recommended Threads, making it more likely that others will see your thread and interact. This interaction gets comments and upvotes. Potentially, you could earn back the 10 HBD in LEO equivalent.
I also value the option for longer threads.
I haven't made the time to quantify my actual earnings. However, I do see that my earnings are larger than they were prior to subscribing.
My main motivation for subscribing is more about supporting the community.