Hi!
To be honest, you would need to ask yourself additional questions to make a decision between Squad and Scale. Do you have a big library of test cases, do you need to organize them in folders? The same question goes for your test cycles. Do you need to reuse test cases, or parameterize them?
If most of the answers are yes, you should go for Scale even if you do not need cross-project capabilities.
Finally, note that Scale will not impact your Jira instance if you have a lot of test cases because Scale is not using a Jira issue to represent test cases.