Against your own comps, £1,409 is clearly ambitious: it sits well above the £1,148 75th percentile and is nearly 5x the £307 median. That doesn’t make it impossible, but it does mean the asking price needs a very strong justification in terms of build quality, bespoke execution, or unusually serious parts choices.
For a niche custom valve amp, the upside is usually in the craftsmanship and the appeal to a buyer who specifically wants something hand-built and over-engineered rather than a mainstream commercial piece. If the power supply is truly well sorted, the build is clean, and the unit is fully proven, it could be a rewarding buy for the right system—but at this level, I’d want clear evidence of who built it, what components were used, and whether service support is straightforward before paying top money.
Independent perspective — not a price guarantee. Always verify condition, accessories and provenance before purchase.