Back in 2017, the Bitcoin network was processing more than 450,000 transactions per day, which created network congestion, as the miners were prioritizing transactions based on the transaction fee. The ones with a low transaction fee were stuck in the mempool. In times like this, Bitcoin accelerators can become handy.
Sure they do. Problem was that all "free slots" on these accelerators were always used already. So they offered sometimes premium service to buy slot which is weird because it can be also done with standard transaction but with higher fee.
Overall its interesting idea and concept, but free slots are not possible to get while network is congested and there is huge demand.