It highlights a significant issue with the way OPR handles payment failures and attacks, such as those involving probes. Probes are unsuccessful payment attempts that do not carry a cost for the initiator under the Lightning Network protocol but could, under OPR, allow an attacker to exploit the system without incurring fees. The scenario described involves an attacker, Mallory, sending these probes through a node (Bob) to various endpoints, which would typically fail these probes. The concern is that occasional issues downstream could trigger a penalty payment back to Mallory, although it is clarified that in the case of a failure to provide a timely failure message by Bob, there would be no penalty payment from Bob to Mallory. Instead, Mallory would only recover the funds put into the burn output, with Bob's matching funds for the HTLC being returned to him.

Furthermore, the conversation touches on the broader implications of such vulnerabilities, including the potential for denial-of-service (DOS) attacks aimed at disrupting network operations rather than stealing funds. These attacks could cause financial losses for nodes within the transaction path by forcing them to lose the value of the payment without the ability to collect from the corresponding channel. This raises concerns about the trade-offs between the need for high availability and security within OPR as opposed to the current Lightning Network protocols. The discussion suggests that while OPR might be more vulnerable to certain types of attacks due to its short expiry times, it might also reduce the risk by breaking down larger payments into streams of smaller, faster HTLCs.

The email also delves into the economic aspects of using OPR, noting that accidental routing failures could significantly increase routing costs compared to the current Lightning Network system. Despite the higher relative fees mentioned, the initiation of lower base fees for OPR payments—coupled with the absence of on-chain fees for resolving these payments—presents an attractive proposition for users seeking quick resolution of small payments. The analysis hints at a user's potential willingness to pay a nominal fee for the assurance of swift payment processing, underscoring the practical considerations in balancing costs, security, and efficiency in the development and adoption of OPR.