I have used it in the past for all teams, but mainly the Outlook plugin as an easy way for all our sales/bdr team to log their emails. But Marketo has tweaked its product offering in the past couple of years that I am not even sure I am referring to the same "Marketo Sales Insight".
In terms of working the same leads, to me that seems more like a strategy question than a tools question. For example, how are BDRs or Sales assigned the leads they are working? (For that matter, how did Sales end up working leads separately from the workflow of the BDRs?) As long as you (or someone) has a consistent methodology for assigning leads out, you should be able to block them working the same leads.