You actually have a lot of artistic control over the images you create on RBLX/ai. You can create a simple prompt and select options for styles and perspectives such as a Cartoony style with a perspective of Wide-Shot. You can get results you want by using the variations feature, so if you create something that you kind of like, but want more of it, you can generate multiple generations of it.
The difference is you are paying ~$1-2 on ~10 icons or having to pay a reasonable rate ($30+) just for one icon, and $60 for a thumbnail. Those numbers are the average rates from what I’ve seen.
I’ve seen nothing to suggest this is against the Terms of Service. I’ve asked in multiple staff servers. Services like Ro-Pro use a payment plan like this as well.