I am still wondering about the reliability and longevity of the PV tubes; sound notwithstanding...I know from experience that NOS (UK) Mullards were built for the long-haul.
With that being said I do not have any to use in the BHSE at the moment but from what I gather in that circuit they should last many, many years.
So yes, still more expensive than a set of the PV's but not outrageously so; and with this level of amplification the difference in price becomes even more negligible, relatively speaking.
i've never had someone with a BHSE tell me they had a problem with one of the stock Mullard re-issue (Russian) EL34s. if i shipped with PV tubes, it would probably be a disaster. I don't know how much profit would be enough for that to be something i would ever consider.