Revival band.... Because Rimuru's full power healing potions are not OP enough.
Also, where the heck are they getting these disposable monsters? Are they wearing these bands too? I just can't imagine anyone taking a job with the job description being "Be mercilessly killed, repeatably, every day". Feel so sorry for the Skellies.
Also must wonder what the entry cost is going to be. He has to attract people into his dungeon with loot, make the loot worth the pain and fear of death, and make the fee large enough that he still gains a net profit. I doubt the traffic increase from adventures and merchants following them will bring enough profit to counter the loss from free HQ unique items.