You need to be clear about the difference between a Sea Anchor and a Drogue.
I have a Para Anchor on board as well as Builder's bags as back up (make sure they have a hole in the bottom). But I use a milk crate as a drogue, or sometimes a fender, or maybe even just rope towed astern.
I understand that this post will create more questions than answers but there is loads to say about the whole business of towing stuff (or even anchoring to the sea) for you to get a complete answer.
I wonder if whoever makes the UFO34 specify a drogue. It is really all about the conditions you are facing, whether you have the sea room to run before it, what sort of boat you have, and what exactly you are trying to achieve (keep you straight, slow you down).
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A Jordan Series Drogue with the right number of cones for your boat - and attachment points that are strong enough.
If you want to trust your life and your boat to a builders bag in a survival situation then good luck! Why not take a second one to use as a liferaft?