Does this require the merchants (= people accepting payments) to trust the operator? An example would be that the BTC are sent first to the service and merchants receive only 1 transaction per day to their designated address.
I would recommend to let merchants submit a public BIP32 seed key so the service creates the addresses from that and never has access to the actual funds. It can still charge some fees (e.g. "pay the fees or we don't display any address or our own address and keep funds in escrow/cover fees from incoming payments") that way but would not need to have that much trust. Still (by displaying their own addresses) they can mess with their merchants of course.
It would require merchants to trust the operator to an extent, but the BTC are immediately going to be forwarded to the merchant.
The seed key is a good idea. I'll look into it. The plan is to keep it fee free for the foreseeable future.
The main advantage of the service would be for digital items or sites that want users to pay for an account in bitcoin - things like that.