This comment is not intended to find fault or cause argument... The ACK product is a decent ELT, however there are some shortcomings that should be highlighted so that those who are making a purchase decision do so with knowledge.
There have been several instances where the ACK E04 has been triggered inadvertently. ACK has added a static filter to the installation kit to help with some of these undesirable activations, particularly in composite aircraft. We've seen several instances where the E04 is also triggered through EMI/RFI picked up from other devices on the aircraft, in particular transponders. The telephone-style interface cable seems to be the major culprit in these undesired activations. One should give consideration, if installing an E04, to using proper twisted shielded (Mil-C-27500) cable to wire the EO4 to its buzzer and remote control panel.
While my experience with the Kannad products has been fantastic, the company has drastically increased the pricing of their replacement battery packs. I haven't yet had an opportunity to talk with them directly on this point but will be taking this concern to them as it is a significant cost driver in the overall ownership costs of the unit.
One ELT that has caught my attention of late is the new ARTEX unit, the 345. I've long been a hater of ARTEX and have made no attempt to hide that strong dislike here in this forum. After spending some time with ARTEX reps I'm starting to believe the company, after having been bought and sold several times, is finally back on track. I've also seen several reasons to believe their product is also back on track after having been off in the weeds for a decade or so.
With respect to ADSB out, keep in mind that while we might believe Big Brother is watching us, the reality is that Big Brother only knows the position updates from ADSB have stopped. That could be because we've landed at a buddy's grass strip, or because we've inadvertently turned our airplane into a lawn dart. The ELT still provides a huge benefit in terms of its ability to sound the alert when something has gone wrong. That's why it's still mandated for installation and why there's no plan on the books to remove that mandate.