I think there’s some merit to trialing 2 different HAs at the same time, AS LONG AS, you have plenty of time to try both of them out. The way I would do it is spend a whole month with just one set, or until I have a pretty good idea of what to expect from it (maybe take up to 2 months if necessary). Then spend the next month or two with the second set. Then in the end, once you know what to expect from both after a long adjustment period from both, you can start doing A/B comparison.
Because the Costco HAs have the longest trial period (180 days) as well as the (more likely) lower price, I would start out with the Costco HAs first for a month or two. Then hold on to the Costco HAs while you start trialing the other pair with the place you’ve been dealing with. If you get 30 day trial from the other place, then spend 2 or 3 weeks getting used to them, and spend the last week or two doing A/B comparison. If you get 60 day trial from the other place, that’s even better -> more time for A/B.
Hopefully by that time you’ll be able to form an opinion of which one you like better. If you think they’re about the same, keep the Costco (assumably cheaper). If you like the Costco ones better, then of course keep the Costco. Then you’ll have a few more months left to change your mind on the Costco even.
But if you like the other ones better, then keep both and continue to do A/B until the Costco trial nears the end then the return the Costco. This way, maybe you’ll be able to confirm that you made the right decision by keeping the other pair, confirmed further through a longer A/B period. If somehow you change your mind later and like the Costco ones better, but you already kept and are stuck with the other ones, then return the Costco but at least you now know more what you like and don’t like about both for the next round of purchase a few years later down the road.