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I hadn't used them before though so didn't fancy my chances
At worst you'll have to stick in a tube anyway and you've tried them out.
If you can fix from the outside it means you keep the tyre seated, don't lose (as much) sealant, don't need to use a tube (which might flat further along anyway) and don't cover everything in jizz.
I really should've used my old Horizons to hack a big cut in and see how effective multiple anchovies and/or dynaplugs were - then I'd at least have experience without being out in the field (literally).
I've not done it but I've seen people use more than one plug for longer cuts.