Bitcoin Transaction Accelerators are the enhancers, which are an off-chain service, accepting an extra fee to include a particular transaction in the upcoming Bitcoin block deliberately in order to get sufficient confirmations. These accelerators are run by none other than the miners themselves as their intention is to get higher block mining fees and rewards.
Most of these accelerators you find online are actually NOT ran by miners, but rather just by someone who's looking to make some adrevenue money.
Their sites, or "accelerators" do nothing but either rebroadcasting your transaction, or trying to add them to the VIABTC accelerator (which is nearly impossible, as they're usually filled the second the next hour goes in. (Or that's how it used to be at least.)
And BTC.COM is actually ridiculously expensive. A much better and cheaper solution would be to stop using f*** web wallets, and use a wallet that actually has RBF & segwit.