Historical reference- Defy Gravity Tether: has quick start guide, necessary hardware and some extras. Brand new, never flown or tested. Sold at $70 plus postage.
I'm just a satisfied customer, no relationship to the company nor to Mr. Kinsey.
I have two Tethers and they have always performed flawlessly. Used one on my L3. About a tenth of a gram of BP to open up the Tether, rather than the 4-5 grams I'd have had to use for deploying the main. (A third Tether was consumed by a rocket-eating tree or something. Along with a 6-grain 38mm research case, a G-Wiz altimeter, and a very nice parachute, in a 4" Patriot on its first flight. Never found it. )
And if by some error the thing fires before it's launched, no flying nose cone or ebay that could injure me, or perhaps be seriously damaged by striking me in the head. Just a 'pop' from that tiny BP charge. A new ematch and repacking of the chute/burrito would be required, of course.
Yes, I like my Tethers very much. And wish that Defy Gravity was still in operation...