The sound signatures have some differences: the ART series is warmer, while the Horizon series is more neutral and natural.
In terms of lifespan, the Horizon mini tubes all adopt the latest internal reinforcement structure technology, which indeed results in a longer lifespan.
@alightronics, Thank you for the details.
Based on what you mentioned above, it looks like the Horizon is the better series, at least for my requirements.Not sure why anyone would want to buy the ART series tube. Unless they want some warmth in their bright system?