I;ve not tried the airways plus but I'd always go with global herbs, I use the TB calmer and Laminitis prone supplement and have used acid x and immuplus too - they always seem do exactly what they claim to do and they're definitely my 1st choice now if I need a supplement.
For a breathing supplement I now use Secreta Pro by Equistro - recommended by vet, non prescription - seems to work really well. Used to use Winergy Ventil-ate that was good as well.
Sorry, can't help on Airways plus or Respirator as always used these other two xx
used one tub of respirator but found it expensive but do use there respirator boost some times started on airway plus which i was happy with but my supplier did not have it all the time using feel good 30 breathing now very happy with it
been using global herbs since my boy came off ventipulmin for copd. his breathing is better although recently started coughing occasionally. Have used feel good 30 for the last few days and he seems to be coughing less so i'm not too convinced on the global herbs yet. Not tried Naf product but i had gone to buy that however was out of stock so came away with global herbs instead.