I'm writing an article on hearing protection (OHSA/NIOSH rules, why it matters to audiophiles as well and not just construction workers, musicians, etc.) and reached out to DEC for resources (they make some really cool active attenuation devices; their founder also designed BAs for Sonion); they sent some earplugs with different filters (similar from the common Elacin ER-style filters) that different NRR ratings, as well as the DS-11.
Just a few weeks ago, I could've sworn there were more buying options (such as from their own website), but they seem to have taken away the store listing. I did find an Amazon listing, but the price seems a bit high.
The ACS T15 is also difficult to find this side of the pond, which is perhaps why it quickly became a forgotten commodity within the head-fi carousel. The problem with DEC is like other hearing protection and/or hearing aid companies --- they have trouble appealing to consumers and marketing accordingly.
At this point, even without a direct A/B, I think the ER4 is still the superior choice when it comes to getting that "target response" that so many Ety-heads look for. However, this thing is a nice alternative to it, for people who want just a little more bass depth and a different feel for ergonomics.