Eros is the first, and so far only, Bottlehead product with regulated heater power.
Price is definitely an issue - Foreplay still has to live with its own history (it started at $99!). But probably the biggest issue is the power transformer. In order to use regulated DC heaters, you need a higher power transformer voltage, which makes it not work for AC heaters. Plus, of course, there is the regulator which needs a PC board and heat sink and tantalum caps and a few other parts. The Eros setup can supply only 1.3 amps, using the biggest PC board-mounted heat sink we could find - not enough for SEX, or for a Foreplay with 6SN7s, or for Crack or Smack - all of which use the same power transformer (another cost savings).
That said, we did (last year, I think) about upgrading Foreplay to use the Eros power supply. I wanted to increase the voltage and current in the tubes at the same time, for more headroom and more drive. I suppose that could become an upgrade kit option, too. But we've been trying other approaches to preamps, and some are very promising - enough that we hope to have a completely new preamp eventually. A full-dress Foreplay with C4S's, tube regs, higher voltages, and the Eros power supply would cost the same but not perform as well, so we're putting our efforts into the new design. For the same reason, while I'd love to upgrade the Seduction with Eros power and shunt regulation, it would cost as much as Eros but without delivering the performance to match.
