I've done two of the ACK 406 ELTs now, and I'd go there again. This ELT is easily connected to a GPS, so that its signal transmits present position, which is updated every second, as I recall. They are the least expensive 406 on the market that supports ELT connections, and one of the least expensive on the market period.
First one had a problem with the activation switch, which failed to the "alert" mode. Verified that my antenna and cell phone worked

. Happened to be going into OSH when it happened. Called ACK, and they had a replacement ELT to me via a dealer at the show within two days.
After a couple weeks, they had received the ELT that'd failed, and they called me to let me know what they'd found from the old switch. Very good customer support....they never asked questions....I called and told them the thing failed, and they said they'd have me a new unit pronto. They did. That one has worked for three or four years now.
New plane has one as well. No problems. Haven't crashed recently, so don't know if it'll work with the plane upside down and on fire, but...I think I'll leave that to another day.
Good unit. I wouldn't pay twice as much for one with a built in GPS, personally.
MTV