A story I heard from a former HRB preparer was a situation where a mistake on the return was found after it was filed. The client owed several thousand more in tax. The "Peace of Mind" paid the tax as well as the P&I. My professional liability policy is not designed to pay a tax deficiency.
I know it is a "nothing burger" to offer the Protection Plus, but like Max said, some clients feel better to know that they had the option. If they don't elect to purchase, then they are on notice if something goes wrong, it was their choice to decline the extra service. Otherwise, we do charge to hand hold our clients if they are audited. We do not pay tax. We will pay P&I only if the client allows us to dispute the penalty with the IRS.
I am leaning toward offering the Protection Plus and having each client pro-actively deciding to "opt out." At this point, I don't know what, if any, commission is paid to us if we actually sell one of these policies.