Isn't the idea of soft shackles to use them in static pulls? Not that you had another option, just wondering if it's advised on dynamic pulls.
Not a last resort option at all. I prefer a static recovery any time I can, but given a good recovery point I don't see an issue with soft shackles in a dynamic recovery. I like them over steel shackles in dynamic situations for safety alone. K rope is great option to recover vehicles and is relatively quick. If something were to fail (recovery point, rope, shackle, etc), I'd much rather have a soft shackle attached to that k rope than a steel one.
I had this discussion with the guy in our group that owns a rigging company. He doesn't see any issue either in using them in both static and dynamic situations either. I'm actually headed up next month to his shop to do some testing on some gear. He's got all kinds of cool testing tools for breaking strengths in different situations/applications.
I plan on ordering quite a few more for our kits. I've already had quite a few military and state groups looking them to add them to their kits. Based on weight and ease of use on "unknown" vehicles is huge. Not all recovery points are easy to connect to and the soft shackles provide a good solution to that.
I think people get a little wary of synthetic line when it appears to be "worn"/fuzzy. This doesn't compromise the line. Only when a strand is cut is when you have to replace it like any synthetic line.
I remember when people (Kyle for one) were making fun of synthetic winch line back in the day.
EDIT: This isn't to say I wouldn't suggest keeping steel ones. I would/will for sure. There are some recovery points that just don't lend themselves to being friendly to the synthetic line. We know our training trucks quite well, so it's easy to know what will work where. It's those times when you're with a group or traveling somewhere unfamiliar where I see them being extremely helpful.